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 A287409 #4 May 25 2017 17:54:37
%S A287409 2,5,9,12,14,17,21,23,26,30,32,35,39,41,44,47,50,54,57,59,62,65,68,72,
%T A287409 75,77,80,84,86,89,92,95,99,102,104,107,111,113,116,120,122,125,128,
%U A287409 131,135,137,140,144,147,149,152,156,158,161,165,167,170,173,176
%N A287409 Positions of 1 in A287407.
%C A287409 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 1, 1, 0, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 1, 1, 0, 0, 1, with 0 in positions given by A287410.
%H A287409 Clark Kimberling, <a href="/A287409/b287409.txt">Table of n, a(n) for n = 1..10000</a>
%t A287409 s = Nest[Flatten[# /. {0->{0, 1, 2}, 1->{2, 1, 0}, 2->{2, 0, 1}}] &, {0}, 9]; (*A287407*)
%t A287409 Flatten[Position[s, 0]]; (*A287408*)
%t A287409 Flatten[Position[s, 1]]; (*A287409*)
%t A287409 Flatten[Position[s, 2]]; (*A287410*)
%Y A287409 Cf. A287407, A287408, A287410.
%K A287409 nonn,easy
%O A287409 1,1
%A A287409 _Clark Kimberling_, May 25 2017