OFFSET
0,3
REFERENCES
J. H. Conway and N. J. A. Sloane, "Sphere Packings, Lattices and Groups", Springer-Verlag, p. 110 and 116.
LINKS
John Cannon, Table of n, a(n) for n = 0..5000
J. H. Conway and N. J. A. Sloane, Low-Dimensional Lattices I: Quadratic Forms of Small Determinant, Proc. Royal Soc. London, Series A, 418 (1988), 17-41.
G. Nebe and N. J. A. Sloane, Home page for this lattice
EXAMPLE
1 + 30*q^4 + 30*q^6 + 132*q^10 + 90*q^12 + 270*q^16 + 140*q^18 + 420*q^22 + ...
MATHEMATICA
al[n_, l_, p_, nn_] := Sum[Exp[-2 Pi I k l/n] EllipticTheta[3, Pi k/n, q^p]^n, {k, n}] / n / Sum[q^(p n (m + l/n)^2), {m, -nn, nn}] + O[q]^nn;
as[n_, s_, nn_] := CoefficientList[FullSimplify[Normal@Sum[al[n, l, n/s, nn], {l, s, n, s}]], q];
as[6, 1, 30] (*A023917*)
as[6, 2, 30][[;; ;; 2]] (*this sequence*)
as[6, 3, 30] (*A125561*)
(* Andrey Zabolotskiy, Feb 17 2022 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jan 31 2007
EXTENSIONS
Typo in name corrected by Andrey Zabolotskiy, Feb 16 2022
STATUS
approved