OFFSET
0,2
COMMENTS
a(n) = number of integer lattice points inside the n-dimensional hypersphere of radius n.
LINKS
Eric Weisstein's World of Mathematics, Jacobi Theta Functions
FORMULA
a(n) = A122510(n,n^2).
MATHEMATICA
Table[SeriesCoefficient[EllipticTheta[3, 0, x]^n/(1 - x), {x, 0, n^2}], {n, 0, 19}]
Table[SeriesCoefficient[1/(1 - x) Sum[x^k^2, {k, -n, n}]^n, {x, 0, n^2}], {n, 0, 19}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Apr 14 2018
STATUS
approved