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 A104104 #11 Oct 13 2019 10:17:33
%S A104104 1,0,1,0,0,1,0,1,1,0,1,0,0,1,0,1,1,0,1,0,0,1,0,1,1,0,1,0,0,1,0,1,0,1,
%T A104104 0,1,1,0,1,0,0,1,0,1,1,0,1,0,0,1,0,1,1,0,1,0,0,1,0,1,1,0,1,0,1,0,1,0,
%U A104104 0,1,0,1,1,0,1,0,0,1,0,1,1,0,1,0,0,1,0,1,1,0,1,0,0,1,0,1,0,1,0,1,1,0,1,0,0
%N A104104 a(1) = 1, if A(k) = sequence of first 2^(k-1) terms and if B(k) is A(k) with 0's and 1's exchanged, then A(k+1) = A(k)A(k) if a(k) = 0, A(k+1) = A(k)B(k) if a(k) = 1.
%t A104104 f[l_]:=Join[l,If[l[[Log[2,Length[l]]+1]]==0,l,1-l]];Nest[f,{1},7] (* _Ray Chandler_, Apr 05 2009 *)
%Y A104104 Cf. A104105, A104106, A104107, A104108.
%K A104104 easy,nonn
%O A104104 1,1
%A A104104 _Leroy Quet_, Mar 04 2005
%E A104104 Edited and extended by _Ray Chandler_, Apr 05 2009