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 A287557 #4 May 31 2017 16:14:24
%S A287557 1,8,10,15,20,22,27,29,35,37,44,46,50,55,57,64,68,70,75,77,83,85,92,
%T A287557 94,98,103,105,112,113,120,122,127,130,135,137,144,145,152,154,159,
%U A287557 164,166,171,173,179,181,188,190,195,197,204,206,210,215,217,224,225
%N A287557 Positions of 0 in A287556.
%C A287557 a(n) - a(n-1) is in {1,2,3,4,5,6,7} for n >= 1; also, 4n - a(n) is in {0,1,2,3} for n >= 1. The first 20 numbers 4n - a(n) are 3, 0, 2, 1, 0, 2, 1, 3, 1, 3, 0, 2, 2, 1, 3, 0, 0, 2, 1, 3, with
%C A287557 0 in positions given by A287558,
%C A287557 1 in positions given by A287559,
%C A287557 2 in positions given by A287560,
%C A287557 3 in positions given by A287557.
%H A287557 Clark Kimberling, <a href="/A287557/b287557.txt">Table of n, a(n) for n = 1..10000</a>
%t A287557 s = Nest[Flatten[# /. {0 -> {0, 1, 3, 2}, 1 -> {1, 3, 2, 0}, 2 -> {3, 2, 0, 1}, 3 -> {2, 0, 1, 3}}] &, {0}, 9]; (* A287556 *)
%t A287557 Flatten[Position[s, 0]]; (* A287557 *)
%t A287557 Flatten[Position[s, 1]]; (* A287558 *)
%t A287557 Flatten[Position[s, 2]]; (* A287559 *)
%t A287557 Flatten[Position[s, 3]]; (* A287560 *)
%Y A287557 Cf. A287556, A287558, A287559, A287560.
%K A287557 nonn,easy
%O A287557 1,2
%A A287557 _Clark Kimberling_, May 31 2017