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 A231923 #7 Nov 16 2013 14:15:20
%S A231923 0,5,1,4,16,6,2,8,17,10,3,7,13,19,12,20,15,21,9,18,24,33,36,64,26,31,
%T A231923 38,41,55,61,65,22,11,14,23,29,43,46,48,53,58,63,67,27,30,39,45,54,57,
%U A231923 66,25,32,37,42,47,59,62,68,34,40,51,60,69,28,49,52,71,35,44,50
%N A231923 Terms of A231922 written in base 10: the binary expansions of a(n) and a(n+1) taken together can be rearranged to form a palindrome.
%C A231923 See A231922 for precise definition.
%C A231923 This is a permutation of the nonnegative integers - see the Comments in A228407 for the proof.
%t A231923 a[0] = 0; a[n_] := a[n] = Block[{k = 1, idm = IntegerDigits[ a[n - 1], 4], t = a@# & /@ Range[n - 1]}, Label[ start]; While[ MemberQ[t, k], k++]; While[ Select[ Permutations[ Join[ idm, IntegerDigits[k, 4]]], #[[1]] != 0 && # == Reverse@# &] == {}, k++; Goto[ start]]; k]; s = Array[a, 60, 0]
%Y A231923 Cf. A230892, A231921, A231925, A231927, A231929, A231931, A231933, A228407, A231922.
%K A231923 nonn,base,easy
%O A231923 0,2
%A A231923 _N. J. A. Sloane_ and _Robert G. Wilson v_, Nov 15 2013