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 A162504 #4 Mar 30 2012 18:51:04 %S A162504 1,17,33,8,24,7,44,52,57,5,9,13,29,4,20,6,42,50,41,21,25,68,14,43,73, %T A162504 76,80,18,45,2,3,15,90,92,22,47,77,99,102,12,16,59,94,65,79,101,110, %U A162504 30,51,28,32,74,23,91,111,117,34,53,83,39,40,78,63,109,118,123,36,38,72,46,48 %N A162504 A162502(A162502(n)). %C A162504 Inverse of A162503: a(A162503(n)) = A162503(a(n)) = n; %C A162504 A162502(n) = A162501(a(n)) = a(A162501(n)). %H A162504 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %K A162504 nonn %O A162504 1,2 %A A162504 _Reinhard Zumkeller_, Jul 05 2009