[Question]
  [
# Cops section
The robbers section can be found [here](https://codegolf.stackexchange.com/q/88981/34388).
Thanks to **FryAmTheEggman**, **Peter Taylor**, **Nathan Merrill**, **xnor**, **Dennis**, **Laikoni** and **Mego** for their contributions.
---
### Challenge
Your task is to write 2 different programs ([full programs/functions/etc.](http://meta.codegolf.stackexchange.com/a/2422/34388)) in the **same** language and the **same** version (e.g. Python 3.5 ≠ Python 3.4, so that is not allowed), and when given **n** (using [STDIN/function arguments/etc.](http://meta.codegolf.stackexchange.com/q/2447/34388)), compute **a(n)** where **a** is an OEIS sequence of your choice. One of those programs is shorter than the other. You only need to submit the *longer* program of the two. The other one needs to be saved in case of not being cracked after 7 days. Your submission is cracked when your program has been outgolfed (whether it is by 1 byte or more).
For example, if the task you chose was to perform **2 × *n***, this could be a valid submission (in Python 2):
> 
> ## Python 2, 16 bytes, score = 15 / 16 = 0.9375
> 
> 
> 
> ```
> print(2*input())
> 
> ```
> 
> Computes [A005843](https://oeis.org/A005843), (offset = 0).
> 
> 
> 
If your submission has been cracked, then you need to state that in your header like so:
> 
> ## Python 2, 16 bytes, score = 15 / 16 = 0.9375, [cracked] + link
> 
> 
> 
> ```
> print(2*input())
> 
> ```
> 
> Computes [A005843](https://oeis.org/A005843), (offset = 0).
> 
> 
> 
---
### Offset
This can be found on every OEIS page. For example, for [A005843](https://oeis.org/A005843), the offset is `0,2`. We only need to use the first one, which is `0`. This means that the function is defined for all numbers ≥ 0.
In other words, the function OEIS(n) starts with **n = 0**. Your program needs to work for all cases given by OEIS.
More information can be found [here](http://oeis.org/wiki/Offsets).
---
### Scoring
The score you get for your submission is equal to the following formula:
**Score** = **Length (in bytes) of secret code** ÷ **Length (in bytes) of public code**
The example above has the score 15 ÷ 16 = 0.9375.
The submission with the **lowest** score wins. Only submissions that have posted their solution will be eligible for winning.
---
### Rules
* The task you need to do is an OEIS sequence of your choice.
* Given **n**, output **OEIS(n)**. Deviation is **not** allowed, so you need to produce the exact same sequence (when given n, you need to output OEIS(n)).
* Submissions that are not cracked within a period of 7 days are considered **safe** after the **solution has been posted** (submissions older than 7 days that do not have their solution posted are still vulnerable in being cracked).
* In your submission, you need to post the following things: **language name**, **byte count**, **full code**, so no pastebin links etc. (to prevent answers like Unary), **OEIS sequence**, **score with lengths of both programs** and additionally, the encoding that is used.
* Note: the same sequence **cannot** be posted twice in the *same* language. (For example, if the sequence A005843 has been done in Pyth, you cannot use Pyth again for that same sequence.)
* Input and output are both in decimal (base 10)
### Leaderboard
```
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script><style>table th,table td{padding: 5px;}th{text-align: left;}.score{text-align: right;}table a{display: block;}.main{float: left;margin-right: 30px;}.main h3,.main div{margin: 5px;}.message{font-style: italic;}#api_error{color: red;font-weight: bold;margin: 5px;}</style> <script>QUESTION_ID=88979;var safe_list=[];var uncracked_list=[];var n=0;var bycreation=function(x,y){return (x[0][0]<y[0][0])-(x[0][0]>y[0][0]);};var byscore=function(x,y){return (x[0][1]>y[0][1])-(x[0][1]<y[0][1]);};function u(l,o){jQuery(l[1]).empty();l[0].sort(o);for(var i=0;i<l[0].length;i++) l[0][i][1].appendTo(l[1]);if(l[0].length==0) jQuery('<tr><td colspan="3" class="message">none yet.</td></tr>').appendTo(l[1]);}function m(s){if('error_message' in s) jQuery('#api_error').text('API Error: '+s.error_message);}function g(p){jQuery.getJSON('//api.stackexchange.com/2.2/questions/' + QUESTION_ID + '/answers?page=' + p + '&pagesize=100&order=desc&sort=creation&site=codegolf&filter=!.Fjs-H6J36w0DtV5A_ZMzR7bRqt1e', function(s){m(s);s.items.map(function(a){var he = jQuery('<div/>').html(a.body).children().first();he.find('strike').text('');var h = he.text();if (!/cracked/i.test(h) && (typeof a.comments == 'undefined' || a.comments.filter(function(b){var c = jQuery('<div/>').html(b.body);return /^cracked/i.test(c.text()) || c.find('a').filter(function(){return /cracked/i.test(jQuery(this).text())}).length > 0}).length == 0)){var m = /^\s*((?:[^,;(\s]|\s+[^-,;(\s])+).*(0.\d+)/.exec(h);var e = [[n++, m ? m[2]-0 : null], jQuery('<tr/>').append( jQuery('<td/>').append( jQuery('<a/>').text(m ? m[1] : h).attr('href', a.link)), jQuery('<td class="score"/>').text(m ? m[2] : '?'), jQuery('<td/>').append( jQuery('<a/>').text(a.owner.display_name).attr('href', a.owner.link)) )];if(/safe/i.test(h)) safe_list.push(e);else uncracked_list.push(e);}});if (s.items.length == 100) g(p + 1);else{var s=[[uncracked_list, '#uncracked'], [safe_list, '#safe']];for(var i=0;i<2;i++) u(s[i],byscore);jQuery('#uncracked_by_score').bind('click',function(){u(s[0],byscore);return false});jQuery('#uncracked_by_creation').bind('click',function(){u(s[0],bycreation);return false});}}).error(function(e){m(e.responseJSON);});}g(1);</script><link rel="stylesheet" type="text/css" href="//cdn.sstatic.net/Sites/codegolf/all.css?v=7509797c03ea"><div id="api_error"></div><div class="main"><h3>Uncracked submissions</h3><table> <tr> <th>Language</th> <th class="score">Score</th> <th>User</th> </tr> <tbody id="uncracked"></tbody></table><div>Sort by: <a href="#" id="uncracked_by_score">score</a> <a href="#" id="uncracked_by_creation">creation</a></div></div><div class="main"><h3>Safe submissions</h3><table> <tr> <th>Language</th> <th class="score">Score</th> <th>User</th> </tr> <tbody id="safe"></tbody></table></div>
```
> 
> **Note**
> 
> 
> This challenge is finished. The final winner is **feersum** with his [*Seed answer*](https://codegolf.stackexchange.com/a/98599/34388). Congratulations! :).
> 
> 
> You can still submit new cops, but be aware that they are no longer competing.
> 
> 
> 
  
[Answer]
# [Seed](http://esolangs.org/wiki/Seed), 5861 bytes, score = 5012 / 5861 = 0.85
The sequence is primes ([A000040](http://oeis.org/A000040)) with offset 1. a(1) = 2, a(2) = 3, a(3) = 5 etc.
```
106 4339425277766562922902283581834741289660008085947971671079664775075736459902652798498038280771739790213868067702391567527146683746696872737118568202495046682058807677834082334206717794057290386357040004038910321326390033894692316122893125849512049817771469697446796247656883761642659391998672259889315862253584980121050081936190889196979721443972131545258528161479083569474217100401074866410321578452749003295370495810488337344650619973376676577461877392643228932028285261311284691649403036725905675576380944186859525020321196255472295415627414823269713084816196540461818684672201926996228242729726187404845487167114556965625764494860789841409004737497250600337038738035289643512265772877903971230007222865264200102217827010958702813633039465646713707971175729900391272165457566364779628858903697222589748797809421482136725017988969980267265196209027326008642464190920825439635011414535065156799655809935871795742526416544853103823906918352472744460644939241345215614650110978624804796257165525598653433482592675123776747497586586903140407616610040250976121531777891358439091358523224019193934111409521776865798864774150127996987606796522094617839125169013781373842026970010007574244564780540958252950607459585834584855526028427463655493110963000525209314274839412714497954647707284352161251044088451086878301225167181712809612927720502228546704347274977503482518386819117870800284276687560241308964641752876311905619184965236937789822712948719170589044519552259399272657757694404103028213338440810122219269214268424256451648966039627998513353115348057963135398345514276156595104642595820063441019481255889600472121104059631555738973905087895006671206400595057069658845297458058584470727379036742268107372233190371861824194831387484478317333784774872796689435056263039565495723444232483369405079512770383639748492508848098080619713255928884946598796741958520788406091704951276729428229224292748702301286318784744573918534142896761450194446126776354892827260482520089107240497527796383449573487121759294618654056309957794765646022274249211113876873102681817500947681708211056388348991201016699342850495527766741633390367735662514559206616070479934780700857859919517187362382258597709910134111383911258731633002354208155277838257255571878219168563173495861133946240923601273185050088148273459064040178741322137494758164795598458780786653602794809987537740537018415433767449108362051063814315399931951925462073202072886716208053889630274798247936580024665863765351912184189125660586187615847325588786048095120241198943086897428919324650596915625795076460123743259068671341944912206659194476673792489442514470540309819938731582497982088632076086088279435186513066668502875362808653657423813387124496122632219269226944975782747969308509448942429277233562654639293567532567668357917753810024961683829653277391094269518376510962710057956994339018307344554672056556222387849272880157861877494719706801624724491116189525394408237355854147113614645956561900837121715298276123085019204014577395795131906357190097536924932784935203378709529040555114884933996346694363879974847691625806412083107877442577777402405491226347699452398189866905599648314105255526411599513768016126067224570735746339691839657336828937030584950250402550603260483421505256395736457980708347396132620971927806636308105501893575073944959824958733880580825249931469481777083600987966500968473202481877213198175820182125298036242272662171321630056435823478710070315022531849275633515412140708923196338877549535352180465031450246889723670908173572778497329815806296369714467774385173078365517895215622645081749679859298824530173433952201710212962315524645807786760255396609101229899503687886977229729747349967302227815724222900649259120496955396616388023947812556426182596252076072286860171961582235043470190275528327438941205680729222092142315348205283459886659277456757338926863444370956987436702675569004062857510888080701482282900718067707825890168959050535970636214821273965900140346587802750221148933877600652180282267212515086387728695565345543441575183083490091817551421389124038251086513387106526847199935776240422217886407416027185332010280169564289345500368555274327733580514983967396271907637608170801013991375555069570288329399237332712790289521766624379537848996471168926519414464863388365890585061582441222989105844636887033599262856636618609644981203616618819656730174147506366895579518927217154437260067784133452192099436160162797896733220282837763342940047719962882720310397266700665603774047807673735452896542215047419894928360985667680051383584281780118001522220147385455276205847620842066894760474814386271419398361771509559702341442734727141312211989794380570433135781896005067541537095546614638001539678780066976441749790924521292297473522803115912791790379839635473194794843511234906415092857115568242448079933264380632375450234146479596225552359821776361923588178896354011117990551249184457345201223244319766597339520899930287542362386381372955844126876031262062731835081542890548095759704856479235361996156162229417953890962902505112862674541020677153054937034038823204321411753183982406667628845943390275194956321260584953509501973880059966268311741789559039618821364775407403947492157311255310143283125490988585303127442698159113924719563571459841025286208880511134222538431747221840824203312684036627017414295981003169360893015436564680773233890198618904647085929678054127680367983802905553144716598061593632352021737488422700265144189474970515439967472618438343180405852959047054139020095303915498443045344690691354304662161461750826840689185141612937350984288238847592910919431788170821390987459951181698659544772214696392241600642992000900364649438402093845534643663733216626212187314397293309505677932731383013397665193960914949915855970134736764497124186701371371881061763702617034928084811708964018610410971938419410791443362686750151572343348438861493025667676713
```
The Befunge-98 programs were tested with [this interpreter](http://mearie.org/projects/pyfunge/).
Solution:
```
62 92671758747582594731336103958852355343308794409787718910287760272065096600068486400261521203099179296478278113800406388237579729434074471528101978922110199511009255327569364221068648720732186414156697930516237153253745234146558781777104311285708042469572129997820696177040412749585193035961972308024909384538547357820271391461203855177879703963391294547499579588457829374981409596253284387318191154655397249791533591896711203680125312645807793061567274893660125978667479654664977040722935418267606762108334976561590548772755653088127344268269983549959628254712562135604114391709222466418283973346968039685907258341712475120187026707300070769277380483828579629391533415119380882514570806683534933872011332303802477012040660361613689139008855327957705058672774790021218679288003003953301651226513713984857174365383390364296326192225244927665294515693697694918935732394438095829822147927645949273829493190176397786165741955566462476231578299385726525505407052332068778469428870102672560545990553686935179657522071350801304923521681690806124866463401094200444841941834667455137491597902735287855498886460945851544063102556545691787612423033525861765804657417395955322217721677429700032333887700477665924915189639029356029794151144702621112140447347270986003871777552705154393697526621456025974679633450745341583481291685834000335168972075093212539251102818038917942913311300883294570091156661153874804268309393591292001433191276766990017144340677002050765359295580546228905861008474333888247511333039470305173620221481374758754343560048199433044290376988914313248904786418615239832295700238599693805552407166251501198275363727855984193340187485162706203747898935844148656997727555488455764358003951396850496841760348138874901474547533715922587211143833052692993182786162665394965914056238514702648647904702501871758140636318131208564891924287008550289224318358936576352473100482724524675417108540029486047223784009872784235439805791496176981701859374772960623187174667015174831665360382067784289660747175586412802848517818731070091826086320292632019033525579172665790335268736167170506003176022610987557889205903933680970434653929602313812168432779881423599218075810156457004870273456214668951969634696002866863369645150677406566613367576078149751561615160777945725724620047443832859087000460506626402089973036918592151204779260519899343451226942874643654023265001514280212345984966126290887141500898797940093805650642580450926977375576911590855135774911449619005627413806680159169643085790457809525639117624947749945044091079624534522626841372604654172723500062361904864176709974716350878399949908529715899937417421315012456868864220900338162700464737416505300734198857624165994112815507157337074226022552948626042899845891195024145834980781844015548398775284084741665926642729256313545870065439195137107807599897817556866239630270351410298105991743248934632486671734759038305157913444368204353943206369388913837519310828223093441519335111533635957953613758894822654736600526811789875376813119426924959017038654104216784121093688306563643326587639486472221258233221666454164763738631579246841130247019172136121041002571694545781948282785399495873501148416357057693713305042834246973535325571882393889489457235864027134943913383832461393499203435931881991959787045205816313165984531168137210464591653390767999403651750434079431253272021002273680565508340556736474927770564408343360602057949991306130979603289667991356237787412616305022971197507815004141825394838946364485315703051195195566893733123391158803413838803831010122718476800229685100410524315094662633390222854924884579083098055980542607258318868514903610787510921796157291630993618714015755412239872758443166948699744841899868754369627081727143351807615097715679652005998467491609044596871312950634152039807480021814406950780706131231897491212637759991818212542181136384052857191779658528790835620632765143337026858373660057972387266312097135260115742458792764792668883627539340807572869610941154184473111399152964165437112713815173281951728792354570851956468302291939952274005357250989986640723863408051924618400882866539701190471828299028566020683682444415198672952980294639217217840535225987439355834087974716313911977302809235338769491339553247328065401203243450045946392960085318343121705830317674151229536850726617093615850507955559652374337057819549481320081981520577039493601331233500403284295119207704095876958023271178964331413629547646937335760969491450824461526563643617594783473684358594189269252499897162333533284912320654686655888508024970105099967896167541978181602786701854274646885561632089896312016789257459673121974866871919820865433343707787147414982407950775979279255414469970743690769124215210050618943726165676550098723299244096267839544684847323547847832349290874282817429866612456451105673214159820212156069771415582214200701894487126822756864305461967035982308878073752362075553218935807632264803200753661147341613284071218919438723527468202903770806766095252957940538229987302177328543423522712562396242285027178395886649344
```
[Answer]
# [Jelly](https://github.com/DennisMitchell/jelly), 5 [bytes](https://github.com/DennisMitchell/jelly/wiki/Code-page), score 0.8 (4 / 5) [[cracked!](https://codegolf.stackexchange.com/a/89108/58271)]
```
R²SÆ½
```
Computes [A127721](http://oeis.org/A127721 "A127721 - OEIS").
[Try it online!](http://jelly.tryitonline.net/#code=UsKyU8OGwr0&input=&args=MQ&debug=on)
---
Here's the solution:
```
RÆḊḞ
```
* implicitly take input `n`
* `R`: list from `[1, 2, ..., n]`
* `ÆḊ`: In our case, this will actually return the square root of the sum of squares (which may be useful in future golfing)!
* `Ḟ`: floor the result.
The [documentation](https://github.com/DennisMitchell/jelly/wiki/Atoms) for `ÆḊ` reads:
> 
> `ÆḊ`: Determinant, extended to non-square matrices.
> 
> 
> 
The key is *extended to non-square matrices*. The "determinant" of a non-square matrix is usually undefined, but one reasonable definition is `sqrt(det(A A^T))` (which for a square matrix reduces to `|det(A)|`). In our case, `A A^T` is a 1 x 1 matrix containing the sum of squares. The square root of the determinant of that gives us exactly what we need to shave off the last byte!
[Answer]
## [Retina](https://github.com/m-ender/retina), 28 bytes, score = 0.9286... (26/28), [cracked by feersum](https://codegolf.stackexchange.com/a/89085/8478)
```
.+
$*
^$|^((^|\3)(^.|\1))*.$
```
Computes [A192687](https://oeis.org/A192687), (offset = 0).
[Try it online!](http://retina.tryitonline.net/#code=JShHYAouKwokKgpeJHxeKChefFwzKSheLnxcMSkpKi4k&input=MAoxCjIKMwo0CjUKNgo3CjgKOQoxMAoxMQoxMgoxMwoxNAoxNQ) (The first line enables a linefeed-separated test suite.)
This is the difference between Hofstadter's [male](https://oeis.org/A005378) and [female](https://oeis.org/A005379) sequences. ([Relevant PPCG challenge.](https://codegolf.stackexchange.com/q/80608/8478))
This was my original code:
```
.+
$*
^((^.|\3)(\1)|){2,}$
```
This answer was a bit of a gamble anyway, because the actual solution is based on a regex [I announced to be the shortest known Fibonacci-testing regex](http://chat.stackexchange.com/transcript/240?m=29301239#29301239) in chat a few months ago. Luckily, no one seemed to remember that. :)
[Answer]
## [Stack Cats](https://github.com/m-ender/stackcats), 14 bytes, score = 13 / 14 = 0.929 [[cracked](https://codegolf.stackexchange.com/a/89956)]
That's 10 bytes of code, plus 4 for the arguments  `-nm`.
Computes [A017053](https://oeis.org/A017053). In case OEIS is down, that's `a(n) = 7n + 6`, starting at `n = 0`.
```
![_-_:-_-_
```
The full code (usable without `-m` argument) is `![_-_:-_-_-_-:_-_]!`
The hidden solution was
```
!]|{_+:}_
```
[Answer]
# [Hexagony](https://github.com/m-ender/hexagony), 91 bytes, Score = 0.725274725 (66/91) [[Cracked]](//codegolf.stackexchange.com/a/89095/8478)
Computes [A000045](https://oeis.org/A000045) (Fibonacci sequence, offset 0).
I won't be too surprised if someone manages to beat this and my more golfed version~~, although it should be hard.~~
Edit: Holy cow, @MartinEnder whipped me with a 33 byte solution.
Golfed (91):
```
?\]~<~.{>'"/(@{\''1<{!1>{{1}/}{'\1</={}/_\'0"/>+(}\/}(+'+'%=<>=%"=+("\/+"(+}+<>{{}=~\.....|
```
Formatted:
```
      ? \ ] ~ < ~
     . { > ' " / (
    @ { \ ' ' 1 < {
   ! 1 > { { 1 } / }
  { ' \ 1 < / = { } /
 _ \ ' 0 " / > + ( } \
  / } ( + ' + ' % = <
   > = % " = + ( " \
    / + " ( + } + <
     > { { } = ~ \
      . . . . . |
```
[Try it online!](http://hexagony.tryitonline.net/#code=P1xdfjx-Lns-JyIvKEB7XCcnMTx7ITE-e3sxfS99eydcMTwvPXt9L19cJzAiLz4rKH1cL30oKycrJyU9PD49JSI9KygiXC8rIigrfSs8Pnt7fT1-XC4uLi4ufA&input=NQ)
I'm not going to post an explanation for this, it's too horrible...
Golfed (66):
```
?{1}]0@._.>\>+{./'++.!.|.*'}..\}{\=++.../'"<_}\"+<./{(/\=*"=/>{=+"
```
Formatted:
```
      ? { 1 } ] 0
     @ . _ . > \ >
    + { . / ' + + .
   ! . | . * ' } . .
  \ } { \ = + + . . .
 / ' " < _ } \ " + < .
  / { ( / \ = * " = /
   > { = + " . . . .
    . . . . . . . .
     . . . . . . .
      . . . . . .
```
Colored:
[![Fibonacci sequence](https://i.stack.imgur.com/DQnmf.png)](https://i.stack.imgur.com/DQnmf.png)
[Try it online!](http://hexagony.tryitonline.net/#code=P3sxfV0wQC5fLj5cPit7Li8nKysuIS58LionfS4uXH17XD0rKy4uLi8nIjxffVwiKzwuL3soL1w9KiI9Lz57PSsi&input=MTA)
Explanation:
The memory layout I used looks a little like this:
```
   |
   a
   |
  / \
b+a  b
/     \
      |
    input
```
The initialization (in black) sets a=0 and b=1. Then, the main loop:
* goes from `a` to the input cell - `'"`
* decrements the input - `(`
* adds b and a - `{{=+`
* moves it "out of the way" - `"+{=*`
* sets a to b - `'+`
* moves a "out of the way" - `'+}=*`
* moves b+a back to its original position - `"=+`
* sets b to b+a - `"+`
* moves a back to its original position - `}+`
Once the input cell reaches 0, the MP moves to a, prints, and exits.
What I could have done to save more bytes is to use &, which just sets the current cell to either its left or right neighbor. I also could have had a bit better flow control, but it's okay as it stands.
[Answer]
# [M](https://github.com/DennisMitchell/m), 10 [bytes](https://github.com/DennisMitchell/jelly/wiki/Code-page), score 0.6 (6 / 10) [[cracked](https://codegolf.stackexchange.com/a/89072/12012)]
```
R‘ạḤc’*@RP
```
A tad cheaty since M and Jelly are quite similar, but allowed by the rules. This version is based on [@LeakyNun's crack](https://codegolf.stackexchange.com/a/89065/12012) to my Jelly answer.
This calculates sequence [A068943](http://oeis.org/A068943 "A068943 - OEIS"). [Try it online!](http://m.tryitonline.net/#code=UuKAmOG6oeG4pGPigJkqQFJQCsOH4oKs&input=&args=MSwgMiwgMywgNCwgNQ)
### Intended solution
The following code works in M/Jelly.
```
R¹¡PÐL
```
I actually had a 4-byte solution to which I added some fluff to make it seem more difficult to crack by using brute force.
```
R¡FP
```
[Try it online!](http://m.tryitonline.net/#code=UsKhRlA&input=&args=Ng)
This is the one I'm going to explain.
```
R¡FP  Main link. Argument: n
 ¡    Execute the left to the left n times, updating the return value.
R       Range; map each integer k to [1, ..., k].
      This does the following for the first values of n.
        1 → [1]
        2 → [1,2]   → [[1],[1,2]]
        3 → [1,2,3] → [[1],[1,2],[1,2,3]] → [[[1]],[[1],[1,2]],[[1],[1,2],[1,2,3]]]
  F   Flatten the resulting, nested array.
   P  Take the product of the reulting array of integers.
```
[Answer]
## [Snowman](https://github.com/KeyboardFire/snowman-lang), 50 bytes, score = 0.9 (45 / 50) [[cracked by Lynn](https://codegolf.stackexchange.com/a/89363/3852)]
```
((}#NDe`nOnO|`2nMNdE0nR2aGaZ::nM;aF;aM:nS;aF,nM*))
```
This is a subroutine that takes a number as its argument and returns another number.
Computes [A122649](https://oeis.org/A122649) (offset = 1).
[Try it online!](http://snowman.tryitonline.net/#code=fnZnMTBzQiogLy8gcmVhZCBpbnB1dCBmcm9tIFNURElOIGFuZCBwYXNzIGl0IHRvIHRoZSBzdWJyb3V0aW5lCgooKH0jTkRlYG5Pbk98YDJuTU5kRTBuUjJhR2FaOjpuTTthRjthTTpuUzthRixuTSopKQoKI3RTc1AgICAgLy8gb3V0cHV0IHRoZSByZXR1cm4gdmFsdWUgdG8gU1RET1VU&input=MTA)
[Answer]
## Haskell, 15 bytes, score = 13/15 (0.866) ([cracked](https://codegolf.stackexchange.com/a/92656/20260))
```
f x=1+2*div x 2
```
[A109613](https://oeis.org/A109613) with offset 0. Repeats each odd number twice.
```
1, 1, 3, 3, 5, 5, 7, 7, 9, 9, 11, 11, 13, 13, ...
```
[Answer]
# [Brachylog](https://github.com/JCumin/Brachylog), 27 bytes, score = 0.666... (18/27), [Cracked!](https://codegolf.stackexchange.com/a/89021/41723)
```
+ybL:L:[1]co~c[A:B]hl-?,A*.
```
Computes [A010551](https://oeis.org/A010551) (offset = 0).
You can [try it online here](http://brachylog.tryitonline.net/#code=K3liTDpMOlsxXWNvfmNbQTpCXWhsLT8sQSou&input=MTA&args=Wg).
### Explanation
Since the vast majority of people don't know this language, and since I'm posting this answer mostly to get people looking into it (See: [Brachylog's Wiki](https://github.com/JCumin/Brachylog/wiki)), I'll provide a short explanation of the code above:
```
+           Add 1 to the input N
ybL         L = [1, 2, ..., N+1]
:L:[1]c     Construct a list [1, 2, ..., N+1, 1, 2, ..., N+1, 1]
o           Sort the list from smallest to biggest
~c[A:B]     A concatenated to B results in that sorted list
hl-?,       The length of A is N + 1
A*.         The output is the result of the product of all elements of A
```
[Answer]
## Haskell, 4 bytes / 5 bytes ([cracked by Leaky Nun](https://codegolf.stackexchange.com/a/89046/20260))
Let's start simple. [A000012](https://oeis.org/A000012), the sequence of all 1's (offset 0). Here's a table:
```
0 -> 1
1 -> 1
2 -> 1
3 -> 1
4 -> 1
 ...
```
**5 bytes:**
```
f n=1
```
[Answer]
# Java 7, 53 bytes, score = 0.9623 (51/53) [Cracked](https://codegolf.stackexchange.com/a/89083/58251)
```
int f(int n){return n<1?3:n<2?0:n<3?2:f(n-2)+f(n-3);}
```
Computes the Perrin sequence, [A001608](https://oeis.org/A001608)
```
f(0)=3
f(1)=0
f(2)=2
f(n)=f(n-2)+f(n-3)
```
First code golf attempt, feel free to point out any mistakes.
## Explanation after cracking:
[miles](https://codegolf.stackexchange.com/a/89083/58251) shortened the first three values (0,1,2) -> (3,0,2) to
```
n<2?3-3*n:n<3?2
```
while my own solution was a slightly over-engineered
```
n<3?(n+4)%5*2%5
```
Combining the two tricks, you get
```
n<3?3-3*n%5
```
for a 47-byte
```
int k(int n){return n<3?3-3*n%5:f(n-2)+f(n-3);}
```
which looks pretty compact for Java :)
[Answer]
## Cheddar, 7 bytes, score = 0.8571 (6/7), [[cracked]](https://codegolf.stackexchange.com/a/89053/40695)
```
n->2**n
```
Pretty simple, just the powers of two. [OEIS A000079](https://oeis.org/A000079)
[Try it online!](http://cheddar.tryitonline.net/#code=bi0-Mioqbg&input=NA)
[Answer]
# J, 17 bytes, score = 0.8235 (14/17) ([cracked](https://codegolf.stackexchange.com/a/89029/6710))
```
(+/@(!+:)&i.-)@>:
```
Computes [A002478](http://oeis.org/A002478).
The funny thing is that this version was originally the short one to be kept secret.
[Answer]
# Python 2, 43 bytes, score = 0.9302 (40/43), [cracked](https://codegolf.stackexchange.com/a/89022/45268)
`f=lambda n:n==1or-(-sum(map(f,range(n)))/3)`
Computes [A072493](https://oeis.org/A072493)
Let's see if anybody can golf off all 3 bytes.
[Answer]
## Pyke, 11 bytes, score = 0.45 (5/11) [[cracked]](https://codegolf.stackexchange.com/a/89116/12012)
```
hZRVoeX*oe+
```
Calculates [OEIS A180255](https://oeis.org/A180255)
[Try it here!](http://pyke.catbus.co.uk/?code=hZRVoeX%2aoe%2B&input=4)
[Answer]
# [Jelly](https://github.com/DennisMitchell/jelly), 9 [bytes](https://github.com/DennisMitchell/jelly/wiki/Code-page), score 0.5556 (5 / 9) [[cracked](https://codegolf.stackexchange.com/a/89218/12012)]
```
r©0+’Ac®Ḅ
```
This calculates sequence [A119259](http://oeis.org/A119259 "A119259 - OEIS"). [Try it online!](http://jelly.tryitonline.net/#code=csKpMCvigJlBY8Ku4biECsW8w4figqxH&input=&args=MCwgMSwgMiwgMywgNCwgNSwgNiwgNywgOCwgOSwgMTA)
[Answer]
# [Brachylog](https://github.com/JCumin/Brachylog), 11 bytes, score = 10 / 11 = 0.909, [cracked!](https://codegolf.stackexchange.com/a/89320/41723)
```
ybLrb:Lrcc.
```
Computes [A173426](https://oeis.org/A173426).
[Try it online!](http://brachylog.tryitonline.net/#code=eWJMcmI6THJjYy4&input=MTE&args=Wg)
### Explanation
```
ybL      L = [1, 2, …, Input]
rb       Get [Input - 1, …, 2, 1]
:Lrc     Concatenate [1, 2, …, Input] and [Input - 1, …, 2, 1]
c.       Concatenate [1, 2, …, Input, Input - 1, …, 2, 1] into a single integer
```
[Answer]
# J, 20 bytes, score = 0.75 (15/20) ([cracked](https://codegolf.stackexchange.com/a/90411/6710))
```
[:*/0 1(]{:,+/)^:[~]
```
Computes [A001654](http://oeis.org/A001654).
My solution for 15 bytes was
```
*&(+/@:!&i.-)>:
```
[Answer]
# [Sesos](https://github.com/DennisMitchell/sesos), 14 bytes, score = 0.8571 (12/14) ([cracked](https://codegolf.stackexchange.com/a/88989/48934))
```
0000000: 16f8be 760e1e 7c5f3b 07ddc7 ce3f                  ...v..|_;....?
```
Computes [A000290](https://oeis.org/A000290).
[Try it online!](http://sesos.tryitonline.net/#code=c2V0IG51bWluCnNldCBudW1vdXQKZ2V0CmptcCxzdWIgMSxmd2QgMSxhZGQgMSxmd2QgMSxhZGQgMSxyd2QgMixqbnoKZndkIDEKam1wCiAgc3ViIDEsZndkIDEKICBqbXAsc3ViIDEsZndkIDEsYWRkIDEsZndkIDEsYWRkIDEscndkIDIsam56CiAgZndkIDEKICBqbXAsc3ViIDEscndkIDEsYWRkIDEsZndkIDEsam56CiAgcndkIDIKam56CmZ3ZCAzCnB1dA&input=MTI&debug=on)
### Hints
This binary file has been generated by the following assembler:
```
set numin
set numout
get
jmp,sub 1,fwd 1,add 1,fwd 1,add 1,rwd 2,jnz
fwd 1
jmp
  sub 1,fwd 1
  jmp,sub 1,fwd 1,add 1,fwd 1,add 1,rwd 2,jnz
  fwd 1
  jmp,sub 1,rwd 1,add 1,fwd 1,jnz
  rwd 2
jnz
fwd 3
put
```
[Answer]
## [MATL](https://github.com/lmendo/MATL), 11 bytes, score = 0.8181 (9/11), [cracked](https://codegolf.stackexchange.com/a/89030/36398)
```
YftdA-1bn^*
```
Computes the [Möbius function](https://en.wikipedia.org/wiki/M%C3%B6bius_function), or [A087811](https://oeis.org/A008683) (offset 1).
[Try it online!](http://matl.tryitonline.net/#code=WWZ0ZEEtMWJuXio&input=MTA)
### Resources for robbers
I think this one should be easy, but anyway here is some help.
Code explanation:
```
Yf     % Implicit input. Push array of prime factors, with repetitions
t      % Duplicate
d      % Compute consecutive differences
A      % 1 if all those differences are nonzero, 0 otherwise
-1     % Push -1
b      % Bubble up array of prime factors to the top of the stack
n      % Number of elements
^      % -1 raised to that
*      % Multiply. Implicitly display
```
Language [documentation](https://github.com/lmendo/MATL/tree/master/doc).
MATL [chatroom](https://chat.stackexchange.com/rooms/39466/matl-chatl).
[Answer]
# [Jelly](https://github.com/DennisMitchell/jelly), 11 [bytes](https://github.com/DennisMitchell/jelly/wiki/Code-page), score 0.5455 (6 / 11) [[cracked](https://codegolf.stackexchange.com/a/89065/12012)]
```
Ḷ+’cḶ
r1*ÇP
```
This calculates sequence [A068943](http://oeis.org/A068943 "A068943 - OEIS"). [Try it online!](http://jelly.tryitonline.net/#code=4bi2K-KAmWPhuLYKcjEqw4dQCsW8w4figqxH&input=&args=MSwgMiwgMywgNCwgNQ)
[Answer]
## [MarioLANG](http://esolangs.org/wiki/MarioLANG), 87 bytes, score = 0.839 (73/87), [cracked](https://codegolf.stackexchange.com/a/89213/53880)
```
;
)-)+(< >>
-)===" ""====
>>+([!)( >-(+(
"====#[(("== [
!-) - <!!![)<<)
#======###====:
```
Computes [A000217](https://oeis.org/A000217), the triangular numbers. Offset 0.
[Try it online!](http://mariolang.tryitonline.net/#code=OwopLSkrKDwgPj4KLSk9PT0iICIiPT09PQo-PisoWyEpKCA-LSgrKAoiPT09PSNbKCgiPT0gWwohLSkgLSA8ISEhWyk8PCkKIz09PT09PSMjIz09PT06&input=NQ) 
### Short Solution:
Since the crack took only 1 byte off, I'll share my solution in 73 bytes, which uses a different algorithm altogether:
```
;   +)-<
-   (=="
+)-<(
(=="+
> [!>)[!(
"==#===#[
!    -  <))
#=========:
```
[Try it online!](http://mariolang.tryitonline.net/#code=OyAgICspLTwKLSAgICg9PSIKKyktPCgKKD09IisKPiBbIT4pWyEoCiI9PSM9PT0jWwohICAgIC0gIDwpKQojPT09PT09PT09Og&input=NQ)
**The first program** lays out all the numbers from n to 1 along the tape, then adds up all numbers until it comes across a 0-value cell. It does this by copying each cell into the two adjacent cells, decrementing the right copy, and repeating the process on it until it reaches 0. During this process, the tape looks like this (for n=5):
```
0 0 5 0 0 0 0
0 5 0 5 0 0 0
0 5 0 4 0 0 0
0 5 4 0 4 0 0
0 5 4 0 3 0 0
0 5 4 3 0 3 0
0 5 4 3 0 2 0
0 5 4 3 2 0 2
```
... and so on. Then it moves left, summing the cells until it reaches a cell with 0.
**The second program** only works with three cells of the tape. Until the first cell reaches 0, it does the following: 
* Move the value of the first cell to the second cell.
* Decrement the second cell to 0, adding its own value to the first and third cells.
* Decrement the first cell.
After the first cell reaches 0, the third cell will contain n + (n-1) + (n-2) + ... + 2 + 1.
[Answer]
# [M](https://github.com/DennisMitchell/m), 18 [bytes](https://github.com/DennisMitchell/jelly/wiki/Code-page), score 0.3889 (7 / 18) [[cracked](https://codegolf.stackexchange.com/a/90544/12012)]
```
r0+c
‘Ḥc0r$×Ç:‘+\S
```
This approach is based on [@Sp3000's golf](https://codegolf.stackexchange.com/questions/88981/can-you-outgolf-me-robbers-section#comment220362_90340) of my Jelly answer.
The code calculates sequence [A116881](http://oeis.org/A116881 "A116881 - OEIS") (row sums of **CM(1,2)**). [Try it online!](http://m.tryitonline.net/#code=cjArYwrigJjhuKRjMHIkw5fDhzrigJgrXFMKMHIxMMOH4oKsauKBtyAgICAgICDhuLfigJwgVGVzdCBzdWl0ZS4gUnVucyB0aGUgYWJvdmUgbGluayBmb3IgaW5wdXRzIDAgdG8gMTAu&input=)
[Answer]
## Haskell, 28 bytes, score = 0.3571 (10/28), [cracked](https://codegolf.stackexchange.com/a/97131/20260)
```
f n|odd n=1|1>0=2*f(div n 2)
```
[A006519](https://oeis.org/A006519), the highest power of 2 dividing `n`, starting at `n=1`.
```
1, 2, 1, 4, 1, 2, 1, 8, 1, 2, 1, 4, 1, 2, 1, 16, 1, ...
```
While you get cracking credit for any shorter code, I consider the real puzzle to be getting down to 10 bytes.
[Answer]
## [05AB1E](https://github.com/Adriandmen/05AB1E), 9 bytes, score = 0.6667 (6/9), [Cracked](https://codegolf.stackexchange.com/a/89002/47066)
```
ÐnŠ·sÉO4/
```
Computes: [A087811](http://oeis.org/A087811)
[Try it online](http://05ab1e.tryitonline.net/#code=w5BuxaDCt3PDiU80Lw&input=MjU)
[Answer]
# [Hexagony](http://github.com/mbuettner/hexagony), 7 bytes, score = 0.857 (6/7), [cracked](https://codegolf.stackexchange.com/a/89013/8478)
Not designed to be the winning submission, but definitely a brain cracker. It actually isn't that hard if you think about it :p. Code:
```
\!?__@(
```
Or a more readable version:
```
 \ !
? _ _
 @ (
```
Computes [A052246](https://oeis.org/A052246).
[Try it online!](http://hexagony.tryitonline.net/#code=XCE_X19AKA&input=Nw).
[Answer]
# J, 9 bytes, score = 0.6667 (6/9) ([cracked by Dennis](https://codegolf.stackexchange.com/a/89056/48934))
```
9 o.0j1^]
```
Computes [A056594](http://oeis.org/A056594).
[Answer]
# J, 10 bytes, score = 0.9 (9/10) ([cracked by Dennis](https://codegolf.stackexchange.com/a/89057/48934))
```
*2%~3<:@*]
```
Computes [A000326](http://oeis.org/A000326).
This one should be easy.
[Online interpreter](http://tryj.tk/).
[Quickref](http://code.jsoftware.com/wiki/NuVoc).
[Answer]
## [05AB1E](https://github.com/Adriandmen/05AB1E), 7 bytes, score = 0.571 (4/7), [Cracked](https://codegolf.stackexchange.com/a/89137/47066)
```
0s·Ì3c;
```
Computes: [A006331](http://oeis.org/A006331)
[Try it online](http://05ab1e.tryitonline.net/#code=MHPCt8OMM2M7&input=Nw)
After golfing 5 unique versions of this sequence before finding this public version I hope I haven't left any obvious improvement out there so it'll at least be a challenge for the robbers.
[Answer]
# [M](https://github.com/DennisMitchell/m), 9 [bytes](https://github.com/DennisMitchell/jelly/wiki/Code-page), score 0.6667 (6 / 9) [[cracked](https://codegolf.stackexchange.com/a/89760/12012)]
```
r©0+’Ac®Ḅ
```
A tad cheaty since M and Jelly are quite similar, but allowed by the rules. [@miles' crack](https://codegolf.stackexchange.com/a/89218/12012) to my Jelly answer doesn't work in M; it lacks the `œċ` atom.
This calculates sequence [A119259](http://oeis.org/A119259 "A119259 - OEIS"). [Try it online!](http://m.tryitonline.net/#code=csKpMCvigJlBY8Ku4biECsW8w4figqxq4oKs4oG2auKBtw&input=&args=MCwgMSwgMiwgMywgNCwgNSwgNiwgNywgOCwgOQ)
]