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 A287572 #4 May 31 2017 21:25:06
%S A287572 1,6,12,15,19,21,26,32,34,40,43,45,52,55,57,62,68,71,73,78,81,86,92,
%T A287572 95,99,101,106,112,114,120,123,125,131,133,138,144,146,152,155,157,
%U A287572 164,167,169,174,177,182,188,191,194,200,203,205,212,215,217,222,225
%N A287572 Positions of 0 in A287571.
%C A287572 a(n) - a(n-1) is in {1,2,3,4,5,6,7} for n >= 1; also, 4n - a(n) is in {0,1,2,3} for n >= 1. The first 20 numbers 4n - a(n) are 3, 2, 0, 1, 1, 3, 2, 0, 2, 0, 1, 3, 0, 1, 3, 2, 0, 1, 3, 2, with
%C A287572 0 in positions given by A287573,
%C A287572 1 in positions given by A287574,
%C A287572 2 in positions given by A287575,
%C A287572 3 in positions given by A287572.
%H A287572 Clark Kimberling, <a href="/A287572/b287572.txt">Table of n, a(n) for n = 1..10000</a>
%t A287572 s = Nest[Flatten[# /. {0 -> {0,3,1,2}, 1 -> {3,1,2,0}, 2 -> {1,2,0,3}, 3 -> {2,0,3,1}}] &, {0}, 9]; (* A287571 *)
%t A287572 Flatten[Position[s, 0]]; (* A287572 *)
%t A287572 Flatten[Position[s, 1]]; (* A287573 *)
%t A287572 Flatten[Position[s, 2]]; (* A287574 *)
%t A287572 Flatten[Position[s, 3]]; (* A287575 *)
%Y A287572 Cf. A287571, A287573, A287574, A287575.
%K A287572 nonn,easy
%O A287572 1,2
%A A287572 _Clark Kimberling_, May 31 2017