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 A293811 #8 Oct 20 2017 14:32:17
%S A293811 1,2,1,1,1,2,1,1,2,1,1,2,1,1,1,2,1,1,2,1,2,1,1,1,2,1,1,2,1,2,1,1,1,2,
%T A293811 1,1,2,1,1,2,1,1,1,2,1,1,2,1,2,1,1,1,2,1,1,1,2,1,1,1,2,1,1,2,1,1,2,1,
%U A293811 1,1,2,1,1,2,1,2,1,1,1,2,1,1,1,2,1,1,1,2,1,1,2,1,1,2,1,1,1,2,1,1
%N A293811 "Look twice to the left" sequence starting with 1,2 (see comment).
%C A293811 Stage 0: we start from 1,2.
%C A293811 Stage 1: we add 2 copies of the block to the left of the last term (here the block 1) giving 1,2,1,1.
%C A293811 Stage 2: we add 2 copies of the block to the left of the last term (here the block 1,2,1) giving 1,2,1,1,1,2,1,1,2,1.
%C A293811 Stage 3: we add 2 copies of the block to the left of the last term (here the block 1,2,1,1,1,2,1,1,2) giving 1,2,1,1,1,2,1,1,2,1,1,2,1,1,1,2,1,1,2,1,2,1,1,1,2,1,1,2.
%C A293811 Iterate the process.
%t A293811 Nest[Join[#, Flatten@ ConstantArray[Take[#, Length@ # - 1], 2]] &, {1, 2}, 5] (* _Michael De Vlieger_, Oct 16 2017 *)
%o A293811 (PARI) v=[1,2];for(n=1,10,l=length(v);w=vector(l-1,i,v[i]);v=concat(v,concat(w,w)));a(n)=v[n];
%Y A293811 Cf. A293630.
%K A293811 nonn
%O A293811 1,2
%A A293811 _Benoit Cloitre_, Oct 16 2017