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A350308
a(n) is the constant term in the expansion of Product_{j=1..n} (Sum_{k=-j..j} x^k)^j.
2
1, 1, 13, 2431, 10027503, 1107781071903, 3893880730064443963, 506016205547402043327062969, 2774765502272595019563619139799271431, 722310089115924894687149792741562790592722949523
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