A293811 "Look twice to the left" sequence starting with 1,2 (see comment).

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, 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, 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

Offset: 1

Author

Benoit Cloitre, Oct 16 2017

Keywords

• nonn

Comments

Stage 0: we start from 1,2.

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.

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.

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.

Iterate the process.

Crossrefs

Cf. A293630.

Programs

Mathematica

Nest[Join[#, Flatten@ ConstantArray[Take[#, Length@ # - 1], 2]] &, {1, 2}, 5] (* Michael De Vlieger, Oct 16 2017 *)

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];