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 A308898 #38 Nov 09 2023 08:51:49
%S A308898 0,1,2,3,0,1,2,0,1,2,3,0,1,2,3,0,1,2,0,1,2,3,0,1,2,0,1,2,3,0,1,2,3,0,
%T A308898 1,2,0,1,2,3,0,1,2,3,0,1,2,0,1,2,3,0,1,2,0,1,2,3,0,1,2,3,0,1,2,0,1,2,
%U A308898 3,0,1,2,0,1,2,3,0,1,2,3,0,1,2,0,1,2,3,0,1,2,3,0,1,2,0,1,2,3,0,1,2,0
%N A308898 Fixed point of the morphism 0 -> 01, 1 -> 2, 2 -> 3, 3 -> 012.
%C A308898 This is superficially similar to A014587, although the latter sequence is not well understood. - _N. J. A. Sloane_, Jul 28 2019
%H A308898 Rémy Sigrist, <a href="/A308898/b308898.txt">Table of n, a(n) for n = 0..15126</a>
%H A308898 M. Dekking, <a href="https://arxiv.org/abs/1906.08437">Base phi representations and golden mean beta-expansions</a>, arXiv:1906.08437 [math.NT], June 2019.
%t A308898 Nest[Flatten[ReplaceAll[#,{0->{0,1},1->2,2->3,3->{0,1,2}}]]&,{0},10] (* _Paolo Xausa_, Nov 09 2023 *)
%o A308898 (PARI) M = [[1,2], [3], [4], [1,2,3]]; s = [1]; for (k=1, 100, while (k>#s, s=concat(apply(d -> M[d],s))); print1 (s[k]-1 ", ")); \\ _Rémy Sigrist_, Jul 25 2019
%Y A308898 Cf. A014587. See A309198 for another version.
%K A308898 nonn
%O A308898 0,3
%A A308898 _N. J. A. Sloane_, Jul 24 2019