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 A287001 #4 May 22 2017 20:03:00
%S A287001 4,10,17,21,28,34,41,47,54,58,65,71,78,85,91,98,102,109,115,122,126,
%T A287001 133,139,146,153,159,166,170,177,183,190,196,203,207,214,220,227,234,
%U A287001 240,247,251,258,264,271,277,284,288,295,301,308,315,321,328,332,339
%N A287001 Positions of 2 in A286998.
%H A287001 Clark Kimberling, <a href="/A287001/b287001.txt">Table of n, a(n) for n = 1..10000</a>
%t A287001 s = Nest[Flatten[# /. {0 -> {1, 0}, 1 -> {2, 0}, 2 -> 0}] &, {0}, 9] (* A286998 *)
%t A287001 Flatten[Position[s, 0]] (* A286999 *)
%t A287001 Flatten[Position[s, 1]] (* A287000 *)
%t A287001 Flatten[Position[s, 2]] (* A287001 *)
%Y A287001 Cf. A286998, A286999, A287000.
%K A287001 nonn,easy
%O A287001 1,1
%A A287001 _Clark Kimberling_, May 22 2017