A028649 Expansion of (theta_3(z)*theta_3(21z) + theta_2(z)*theta_2(21z)).

1, 0, 2, 0, 0, 0, 0, 0, 2, 0, 0, 4, 0, 0, 0, 4, 0, 0, 2, 0, 0, 0, 0, 4, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 4, 0, 0, 0, 0, 0, 0, 2, 0, 4, 0, 0, 0, 0, 0, 6, 4, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 4, 2, 0, 4, 0, 0, 0, 0, 0, 0

Offset

0,3

Links

Jinyuan Wang, Table of n, a(n) for n = 0..1000

Mathematica

r[n_]:=Reduce[{x, y}.{{2, 1}, {1, 11}}.{x, y}==n, {x, y}, Integers]; Table[rn=r[n]; Which[rn===False, 0, Head[rn]===Or, Length[rn], Head[rn]===And, 1], {n, 0, 105}] (* Vincenzo Librandi, Feb 23 2020 *)

Prog

(PARI) a(n) = if(n<1, n==0, qfrep([2, 1; 1, 11], n)[n]*2); \\ Jinyuan Wang, Feb 21 2020

Crossrefs

Cf. A028650, A028651, A028652.

Sequence in context: A275962 A132976 A143840 * A305558 A341624 A341620

Adjacent sequences: A028646 A028647 A028648 * A028650 A028651 A028652

Keyword

nonn

Author

N. J. A. Sloane

Status

approved