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 A287203 #4 May 23 2017 21:00:21
%S A287203 1,2,5,6,15,16,19,20,23,24,33,34,43,44,53,54,59,60,65,66,69,70,73,74,
%T A287203 83,84,87,88,91,92,101,102,105,106,109,110,119,120,129,130,139,140,
%U A287203 145,146,151,152,155,156,159,160,169,170,179,180,189,190,195,196
%N A287203 Positions of 2 in A287200.
%H A287203 Clark Kimberling, <a href="/A287203/b287203.txt">Table of n, a(n) for n = 1..10000</a>
%t A287203 s = Nest[Flatten[# /. {0 -> {1, 0}, 1 -> {2, 2}, 2 -> 0}] &, {0}, 11] (* A287200 *)
%t A287203 Flatten[Position[s, 0]] (* A287201 *)
%t A287203 Flatten[Position[s, 1]] (* A287202 *)
%t A287203 Flatten[Position[s, 2]] (* A287203 *)
%Y A287203 Cf. A287200, A287201, A287202.
%K A287203 nonn,easy
%O A287203 1,2
%A A287203 _Clark Kimberling_, May 23 2017