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

1,2

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.

Links

Table of n, a(n) for n=1..100.

Mathematica

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

Prog

(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];

Crossrefs

Cf. A293630.

Sequence in context: A374327 A368473 A106035 * A362228 A105141 A103961

Adjacent sequences: A293808 A293809 A293810 * A293812 A293813 A293814

Keyword

nonn

Author

Benoit Cloitre, Oct 16 2017

Status

approved