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 A287450 #6 May 30 2017 12:14:57
%S A287450 3,4,9,12,15,16,19,24,27,28,33,36,39,40,45,48,51,52,57,60,61,66,67,72,
%T A287450 73,78,81,84,87,88,93,94,99,100,105,108,111,112,117,120,123,124,127,
%U A287450 132,135,136,141,144,147,148,153,156,159,160,163,168,171,174,175
%N A287450 Positions of 2 in A287447.
%C A287450 a(n) - a(n-1) is in {1, 3, 5} for n >= 1; also, 3n - a(n) is in {0, 2} for n >= 1. The first 20 numbers 3n - a(n) are 0, 2, 0, 0, 0, 2, 2, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, with 2 in positions given by A287449.
%H A287450 Clark Kimberling, <a href="/A287450/b287450.txt">Table of n, a(n) for n = 1..10000</a>
%t A287450 s = Nest[Flatten[# /. {0->{0, 1, 2}, 1->{2, 0, 1}, 2->{1, 0, 2}}] &, {0}, 9]; (*A287447*)
%t A287450 Flatten[Position[s, 0]]; (*A189724*)
%t A287450 Flatten[Position[s, 1]]; (*A287449*)
%t A287450 Flatten[Position[s, 2]]; (*A287450*)
%Y A287450 Cf. A287447, A189724, A287449.
%K A287450 nonn,easy
%O A287450 1,1
%A A287450 _Clark Kimberling_, May 30 2017