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 A284885 #4 Apr 17 2017 08:58:16
%S A284885 2,3,5,6,7,8,11,12,14,15,16,17,20,21,22,23,26,27,29,30,32,33,34,35,38,
%T A284885 39,41,42,43,44,47,48,49,50,53,54,56,57,59,60,61,62,65,66,67,68,71,72,
%U A284885 74,75,77,78,79,80,83,84,86,87,88,89,92,93,95,96,97,98
%N A284885 (A284883)/2.
%H A284885 Clark Kimberling, <a href="/A284885/b284885.txt">Table of n, a(n) for n = 1..10000</a>
%t A284885 s = Nest[Flatten[# /. {0 -> {0, 1}, 1 -> {0, 1, 1, 0}}] &, {0}, 6] (* A284878 *)
%t A284885 d = Differences[s] (* A284881 *)
%t A284885 d2 = Flatten[Position[d, 0]] (* A284883 *)
%t A284885 d2/2 (* A284885 *)
%Y A284885 Cf. A284878, A284881, A284883.
%K A284885 nonn,easy
%O A284885 1,1
%A A284885 _Clark Kimberling_, Apr 16 2017