OFFSET
0,3
COMMENTS
a(n) is the coefficient of x^(n^2 * (n+1)/2) in Product_{j=0..n} (Sum_{k=0..2*j} x^k)^n.
MATHEMATICA
a[n_] := Coefficient[Series[Product[Sum[x^k, {k, -j, j}]^n, {j, 1, n}], {x, 0, 0}], x, 0]; Array[a, 9, 0] (* Amiram Eldar, Dec 24 2021 *)
PROG
(PARI) a(n) = polcoef(prod(j=1, n, sum(k=-j, j, x^k))^n, 0);
(PARI) a(n) = polcoef(prod(j=1, n, sum(k=0, 2*j, x^k))^n, n^2*(n+1)/2);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Dec 23 2021
STATUS
approved