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 A231931 #7 Nov 16 2013 14:16:26
%S A231931 0,9,1,8,64,10,2,16,65,18,3,11,25,67,24,72,27,4,12,33,68,32,76,20,34,
%T A231931 74,17,66,80,129,136,512,69,13,5,21,42,77,29,43,75,19,26,81,22,6,14,
%U A231931 49,70,48,78,30,51,89,28,35,92,99,204,225,267,281,515,73,15,7,23,58
%N A231931 Terms of A231930 written in base 10: the binary expansions of a(n) and a(n+1) taken together can be rearranged to form a palindrome.
%C A231931 See A231930 for precise definition.
%C A231931 This is a permutation of the nonnegative integers - see the Comments in A228407 for the proof.
%t A231931 a[0] = 0; a[n_] := a[n] = Block[{k = 1, idm = IntegerDigits[ a[n - 1], 8], t = a@# & /@ Range[n - 1]}, Label[ start]; While[ MemberQ[t, k], k++]; While[ Select[ Permutations[ Join[ idm, IntegerDigits[k, 8]]], #[[1]] != 0 && # == Reverse@# &] == {}, k++; Goto[ start]]; k]; s = Array[a, 60, 0]
%Y A231931 Cf. A230892, A231921, A231923, A231925, A231927, A231929, A231933, A228407, A231930.
%K A231931 nonn,base,easy
%O A231931 0,2
%A A231931 _N. J. A. Sloane_ and _Robert G. Wilson v_, Nov 15 2013