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 A287456 #5 May 30 2017 12:15:38
%S A287456 1,5,9,12,13,17,21,23,25,30,32,34,37,41,45,48,49,53,57,59,61,66,67,71,
%T A287456 73,77,81,84,86,88,93,94,98,100,104,108,109,113,117,120,121,125,129,
%U A287456 131,133,138,140,142,145,149,153,156,157,161,165,167,169,174,175
%N A287456 Positions of 0 in A287455.
%C A287456 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, 1, 0, 0, 2, 1, 0, 1, 2, 0, 1, 2, 2, 1, 0, 0, 2, 1, 0, 1, with 0 in positions given by A287452, 1 in positions given by A287454, and 2 in positions given by A287458.
%H A287456 Clark Kimberling, <a href="/A287456/b287456.txt">Table of n, a(n) for n = 1..10000</a>
%t A287456 s = Nest[Flatten[# /. {0->{0, 1, 2}, 1->{2, 0, 1}, 2->{2, 1, 0}}] &, {0}, 9]; (*A287455*)
%t A287456 Flatten[Position[s, 0]]; (*A287456*)
%t A287456 Flatten[Position[s, 1]]; (*A189666*)
%t A287456 Flatten[Position[s, 2]]; (*A287458*)
%Y A287456 Cf. A287455, A189666, A287458.
%K A287456 nonn,easy
%O A287456 1,2
%A A287456 _Clark Kimberling_, May 30 2017