OFFSET
0,3
MATHEMATICA
a[n_] := Coefficient[Series[Product[Sum[x^k, {k, -j, j}]^j, {j, 1, n}], {x, 0, 0}], x, 0]; Array[a, 10, 0] (* Amiram Eldar, Dec 24 2021 *)
PROG
(PARI) a(n) = polcoef(prod(j=1, n, sum(k=-j, j, x^k)^j), 0);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Dec 23 2021
STATUS
approved