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 A287420 #4 May 26 2017 16:43:38
%S A287420 2,4,7,10,13,17,19,23,25,28,31,35,37,41,43,47,49,52,55,58,62,65,67,70,
%T A287420 73,77,79,82,85,89,91,95,97,101,103,106,109,112,116,119,121,124,127,
%U A287420 131,133,137,139,142,145,148,152,154,158,160,163,166,170,172,176
%N A287420 Positions of 1 in A287418.
%C A287420 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, 2, 2, 2, 2, 1, 2, 1, 2, 2, 2, 1, 2, 1, 2, 1, 2, 2, 2, 2, with 1 in positions given by A287419.
%H A287420 Clark Kimberling, <a href="/A287420/b287420.txt">Table of n, a(n) for n = 1..10000</a>
%t A287420 s = Nest[Flatten[# /. {0->{0, 1, 2}, 1->{1, 2, 0}, 2->{1, 0, 2}}] &, {0}, 9]; (*A287418*)
%t A287420 Flatten[Position[s, 0]]; (*A287419*)
%t A287420 Flatten[Position[s, 1]]; (*A287420*)
%t A287420 Flatten[Position[s, 2]]; (*A287421*)
%Y A287420 Cf. A287418, A287419, A287421.
%K A287420 nonn,easy
%O A287420 1,1
%A A287420 _Clark Kimberling_, May 26 2017