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 A057985 #21 Oct 14 2019 00:10:23
%S A057985 0,1,1,2,1,2,0,1,2,0,0,1,1,2,0,0,1,0,1,1,2,1,2,0,0,1,0,1,1,2,0,1,1,2,
%T A057985 1,2,0,1,2,0,0,1,0,1,1,2,0,1,1,2,1,2,0,0,1,1,2,1,2,0,1,2,0,0,1,1,2,0,
%U A057985 0,1,0,1,1,2,0,1,1,2,1,2,0,0,1,1,2,1,2,0,1,2,0,0,1,0,1,1
%N A057985 Start with 0 and repeatedly substitute: 0->01, 1->12, 2->0.
%C A057985 This is the fixed point of the morphism 0->01, 1->12, 2->0 starting with 0. Let u be the sequence of positions of 0, and likewise, v for 1 and w for 2. Let U, V, W be the limits of u(n)/n, v(n)/n, w(n)/n, respectively. Then 1/U + 1/V + 1/W = 1, where U = 3.079595623491438786010417..., V = 2.324717957244746025960908..., W = U + 1. If n >=2, then u(n) - u(n-1) is in {1,2,3,4,6}, v(n) - v(n-1) is in {1,2,3,4}, and w(n) - w(n-1) is in {2,3,4,5,7}. For n >= 1, the number of terms resulting from n iterations of the morphism is A005251(n+2). - _Clark Kimberling_, May 20 2017.
%H A057985 Clark Kimberling, <a href="/A057985/b057985.txt">Table of n, a(n) for n = 1..10000</a>
%H A057985 <a href="/index/Fi#FIXEDPOINTS">Index entries for sequences that are fixed points of mappings</a>
%t A057985 t = Nest[Flatten[# /. {0 -> {0, 1}, 1 -> {1, 2}, 2 -> {0}}] &, {0}, 10] (* A057985 *)
%t A057985 Flatten[Position[t, 0]] (* A057986 *)
%t A057985 Flatten[Position[t, 1]] (* A057987 *)
%t A057985 Flatten[Position[t, 2]] (* A057988 *)
%t A057985 (* _Clark Kimberling_, May 13 2013 *)
%Y A057985 Cf. A287066 (initial term 1 instead of 0).
%K A057985 nonn
%O A057985 1,4
%A A057985 _Clark Kimberling_, Oct 30 2000