OFFSET
0,1
REFERENCES
J. H. Conway and N. J. A. Sloane, "Sphere Packings, Lattices and Groups", Springer-Verlag, 1999, p. 123.
LINKS
Gabriele Nebe and N. J. A. Sloane, Home page for this lattice.
FORMULA
G.f.: (1/2)*(theta_2^2*theta_3^6 + theta_2^6*theta_3^2).
a(n) = 2*sigma_3(2n+1). - Benoit Cloitre, Apr 12 2003
a(n) = 2 * A045823(n). - Alois P. Heinz, Mar 21 2021
Sum_{k=0..n} a(k) ~ (15*zeta(4)/4) * n^4. - Amiram Eldar, Dec 12 2023
EXAMPLE
2*q^(1/2) + 56*q^(3/2) + 252*q^(5/2) + ...
MATHEMATICA
a[n_] := 2 DivisorSigma[3, 2 n + 1]; Table[a[n], {n, 0, 33}] (* Jean-François Alcover, Jul 06 2017, after Benoit Cloitre *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
EXTENSIONS
More terms from Benoit Cloitre, Apr 12 2003
STATUS
approved