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 A287407 #13 Aug 03 2023 15:28:18
%S A287407 0,1,2,2,1,0,2,0,1,2,0,1,2,1,0,0,1,2,2,0,1,0,1,2,2,1,0,2,0,1,0,1,2,2,
%T A287407 1,0,2,0,1,2,1,0,0,1,2,0,1,2,2,1,0,2,0,1,2,0,1,0,1,2,2,1,0,0,1,2,2,1,
%U A287407 0,2,0,1,2,0,1,2,1,0,0,1,2,2,0,1,0,1
%N A287407 Start with 0 and repeatedly substitute 0->012, 1->210, 2->201.
%C A287407 This is the fixed point of the morphism 0->012, 1->210, 2->201 starting with 0. Let u be the (nonperiodic) sequence of positions of 0, and likewise, v for 1 and w for 2; then u(n)/n -> 3, v(n)/n -> 3, w(n)/n -> 3.
%C A287407 See A287385 for a guide to related sequences.
%H A287407 Clark Kimberling, <a href="/A287407/b287407.txt">Table of n, a(n) for n = 1..10000</a>
%H A287407 <a href="/index/Fi#FIXEDPOINTS">Index entries for sequences that are fixed points of mappings</a>
%e A287407 First three iterations of the morphism: 012, 012210201, 012210201201210012201012210.
%t A287407 s = Nest[Flatten[# /. {0->{0, 1, 2}, 1->{2, 1, 0}, 2->{2, 0, 1}}] &, {0}, 9]; (*A287407*)
%t A287407 Flatten[Position[s, 0]]; (*A287408*)
%t A287407 Flatten[Position[s, 1]]; (*A287409*)
%t A287407 Flatten[Position[s, 2]]; (*A287410*)
%t A287407 SubstitutionSystem[{0->{0,1,2},1->{2,1,0},2->{2,0,1}},0,{5}][[1]] (* _Harvey P. Dale_, Aug 03 2023 *)
%Y A287407 Cf. A287385, A287408, A287409, A287410.
%K A287407 nonn,easy
%O A287407 1,3
%A A287407 _Clark Kimberling_, May 25 2017