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 A287580 #4 Jun 01 2017 21:09:40
%S A287580 2,7,12,13,17,22,27,32,36,37,42,47,51,56,57,62,67,72,73,78,82,87,92,
%T A287580 93,97,102,107,112,116,117,122,127,132,133,138,143,147,152,153,158,
%U A287580 162,167,172,173,177,182,187,192,193,198,203,208,212,213,218,223,227
%N A287580 Positions of 3 in A287576.
%C A287580 a(n) - a(n-1) is in {1,4,5} for n >= 1; also, 4n - a(n) is in {0,1,2,3} for n >= 1. The first 20 numbers 4n - a(n) are 2, 1, 0, 3, 3, 2, 1, 0, 0, 3, 2, 1, 1, 0, 3, 2, 1, 0, 3, 2, with
%C A287580 0 in positions given by A287579,
%C A287580 1 in positions given by A287580,
%C A287580 2 in positions given by A287577,
%C A287580 3 in positions given by A287578.
%H A287580 Clark Kimberling, <a href="/A287580/b287580.txt">Table of n, a(n) for n = 1..10000</a>
%F A287580 a(n) = 4n - A287576(n) for n >= 1.
%t A287580 s = Nest[Flatten[# /. {0 -> {0,3,2,1}, 1 -> {3,2,1,0}, 2 -> {2,1,0,3}, 3 -> {1,0,3,2}}] &, {0}, 9]; (* A287576 *)
%t A287580 Flatten[Position[s, 0]]; (* A287577 *)
%t A287580 Flatten[Position[s, 1]]; (* A287578 *)
%t A287580 Flatten[Position[s, 2]]; (* A287579 *)
%t A287580 Flatten[Position[s, 3]]; (* A287580 *)
%Y A287580 Cf. A287576, A287577, A287578, A287579.
%K A287580 nonn,easy
%O A287580 1,1
%A A287580 _Clark Kimberling_, Jun 01 2017