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 A287403 #4 May 25 2017 17:54:16
%S A287403 2,5,7,10,14,17,20,22,26,29,31,35,37,41,44,47,50,52,55,59,62,65,67,71,
%T A287403 74,77,79,82,86,89,92,94,98,101,104,106,110,112,116,118,122,125,128,
%U A287403 131,133,137,140,142,145,149,152,155,157,161,164,166,170,172,176
%N A287403 Positions of 1 in A287401.
%C A287403 a(n) - a(n-1) is in {2,3,4} for n >= 1; also, 3n - a(n) is in {1, 2} for n >= 1. The first 20 numbers 3n - a(n) are 1, 1, 2, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 1, 1, 1, 1, 2, 2, 1, with 2 in positions given by A287404.
%H A287403 Clark Kimberling, <a href="/A287403/b287403.txt">Table of n, a(n) for n = 1..10000</a>
%t A287403 s = Nest[Flatten[# /. {0->{0, 1, 2}, 1->{2, 1, 0}, 2->{1, 2, 0}}] &, {0}, 9]; (*A287401*)
%t A287403 Flatten[Position[s, 0]]; (*A189728*)
%t A287403 Flatten[Position[s, 1]]; (*A287403*)
%t A287403 Flatten[Position[s, 2]]; (*A287404*)
%Y A287403 Cf. A287401, A189728, A287404.
%K A287403 nonn,easy
%O A287403 1,1
%A A287403 _Clark Kimberling_, May 25 2017