This challenge has two threads. This is the cops' thread. The robbers' thread is located here.

Your challenge is to choose an OEIS sequence and write two full programs in two different languages that produces that nth item in the sequence when given an n via STDIN, or an other forms of standard input, where n is any positive number. However your two programs must be anagrams, meaning each can be rearranged from the other's letters.

Programs must output the decimal of the number followed by optional whitespace to STDOUT. Programs may output to STDERR however it should be ignored and if the hidden case does so it must be clearly stated that this is the case.

If you wish you may also output by character code. However if you do so in your hidden solution you must state such in the body of your submission.

You will then present the OEIS number, the source code for and the name of one language it is in.

Robbers will crack your submission if they find an anagram of the original submission that runs in a language other than the one you already presented. To crack an answer they must only find any language and program which produces the sequence and is an anagram of the original, not necessarily the answer the you were thinking about.

Thus you are incentivized to make it as hard as possible to find any language that does the task using their list of symbols.


This is so the shortest un-cracked program is the winner.


Languages will be considered different if the two proposed solutions do not complete the task in both languages. This will include different versions of the same language as long as neither the cop's solution or the robber's solution produce the correct output in the other's language.

i.e. If the there are two solutions 1 and 2 that are in language A and B respectively solution 2 must not produce the correct output in language A and solution 1 must not produce the correct output in language B.


Once your submission has been uncracked for a week you may post your solution and declare your post safe. If after a week you choose not to post a solution your answer may still be cracked.

  • 4
    \$\begingroup\$ To browse through random OEIS sequences for ideas, go to oeis.org/webcam \$\endgroup\$ – mbomb007 Nov 9 '16 at 18:15
  • \$\begingroup\$ How would it work with languages that like to use flags to the interpreter, such as perl? Are they disqualified? Are flags counted as part of the code? Are flags "free" (not included in code or divulged at all)? \$\endgroup\$ – Emigna Nov 9 '16 at 19:19
  • \$\begingroup\$ Can the hidden program exit with an error (after producing the output)? Should that be indicated in the answer? \$\endgroup\$ – Luis Mendo Nov 9 '16 at 19:34
  • 1
    \$\begingroup\$ Not sure if this would be helpful to anyone else but this highlights any remaining missing characters or any duplicated ones: codepen.io/anon/pen/BQjxRK \$\endgroup\$ – Dom Hastings Nov 11 '16 at 8:12
  • 1
    \$\begingroup\$ It'd be nice if there was a stack snippet to show uncracked answers, oldest first. \$\endgroup\$ – mbomb007 Nov 16 '16 at 15:57

32 Answers 32


05AB1E, 5 bytes, A005843


Calculates n*2.

  • \$\begingroup\$ This is NOT cracked because I just found out that my crack was invalid. I have deleted it now because it is invalid since the original program was a polyglot in 05AB1E/2sable. \$\endgroup\$ – user41805 Nov 13 '16 at 6:05

05AB1E, 5 bytes, A000012 Cracked!


The funny thing is that the cracked version is the intended answer.

Try it online!

  • 1
    \$\begingroup\$ It outputs nothing when the input is 0 \$\endgroup\$ – user41805 Nov 11 '16 at 16:55
  • \$\begingroup\$ And it outputs 21 when input is 42 Here \$\endgroup\$ – user41805 Nov 11 '16 at 16:56
  • \$\begingroup\$ @KritixiLithos There. \$\endgroup\$ – Oliver Ni Nov 11 '16 at 17:10
  • \$\begingroup\$ Now it outputs 1.0 instead of 1 \$\endgroup\$ – user41805 Nov 11 '16 at 17:19
  • 1
    \$\begingroup\$ Cracked! :) \$\endgroup\$ – user41805 Nov 11 '16 at 17:32

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