This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A256618 #4 Apr 05 2015 15:36:48 %S A256618 1,2,3,4,10,5,13,6,7,8,21,9,26,11,12,16,34,14,35,18,15,19,47,17,20,24, %T A256618 25,29,54,22,61,31,23,32,40,27,68,33,28,41,77,30,82,43,38,45,91,39,42, %U A256618 46,36,48,100,50,53,44,37,52,109,51,118,59,58,62,55,60 %N A256618 Index i such that A121217(i) = n, or 0 if no such i exists. %C A256618 If A121217 is a permutation, as conjectured, then this is the inverse permutation. %H A256618 Reinhard Zumkeller, <a href="/A256618/b256618.txt">Table of n, a(n) for n = 1..10000</a> %o A256618 (Haskell) %o A256618 import Data.List (elemIndex); import Data.Maybe (fromJust) %o A256618 a256618 = (+ 1) . fromJust . (`elemIndex` a121217_list) %Y A256618 Cf. A121217. %K A256618 nonn %O A256618 1,2 %A A256618 _Reinhard Zumkeller_, Apr 05 2015