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 A287398 #4 May 25 2017 17:53:40
%S A287398 1,6,8,11,15,16,21,22,26,30,31,35,38,42,43,46,51,53,56,60,61,64,69,71,
%T A287398 75,76,80,83,87,88,91,96,98,102,103,107,111,112,116,119,123,124,127,
%U A287398 132,134,136,141,143,146,150,151,156,157,161,165,166,170,173,177
%N A287398 Positions of 0 in A287397.
%C A287398 a(n) - a(n-1) is in {1,2,3,4,5} for n >= 1; also, 3n - a(n) is in {0,1,2} for n >= 1. The first 20 numbers 3n - a(n) are 2, 0, 1, 1, 0, 2, 0, 2, 1, 0, 2, 1, 1, 0, 2, 2, 0, 1, 1, 0, with 0 in positions given by A287399.
%H A287398 Clark Kimberling, <a href="/A287398/b287398.txt">Table of n, a(n) for n = 1..10000</a>
%t A287398 s = Nest[Flatten[# /. {0->{0, 1, 2}, 1->{2, 1, 0}, 2->{1, 0, 2}}] &, {0}, 9]; (*A287397*)
%t A287398 Flatten[Position[s, 0]]; (*A287398*)
%t A287398 Flatten[Position[s, 1]]; (*A287399*)
%t A287398 Flatten[Position[s, 2]]; (*A287400*)
%Y A287398 Cf. A287397, A287399, A287400.
%K A287398 nonn,easy
%O A287398 1,2
%A A287398 _Clark Kimberling_, May 25 2017