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 A287321 #4 May 23 2017 14:32:30
%S A287321 1,2,6,7,8,12,16,20,22,24,25,26,30,31,32,36,37,38,42,46,50,52,54,55,
%T A287321 56,60,64,68,70,72,73,74,78,82,86,88,90,91,92,96,98,100,101,102,106,
%U A287321 108,110,111,112,116,117,118,122,123,124,128,132,136,138,140,141
%N A287321 Positions of 0 in A287320.
%H A287321 Clark Kimberling, <a href="/A287321/b287321.txt">Table of n, a(n) for n = 1..10000</a>
%t A287321 s = Nest[Flatten[# /. {0 -> {1, 0}, 1 -> {2, 2}, 2 -> 0}] &, {0}, 9] (* A287175 *)
%t A287321 Flatten[Position[s, 0]] (* A287321 *)
%t A287321 Flatten[Position[s, 1]] (* A287322 *)
%t A287321 Flatten[Position[s, 2]] (* A287323 *)
%Y A287321 Cf. A287320, A287322, A287323.
%K A287321 nonn,easy
%O A287321 1,2
%A A287321 _Clark Kimberling_, May 23 2017