OFFSET
0,2
MATHEMATICA
f[n_] := Coefficient[Expand[Sum[(k+1)*x^k , {k, 0, 2n}]^n, x], x, n^2]; Array[f, 15, 0] (* Amiram Eldar, Dec 13 2018 *)
PROG
(PARI) {a(n) = polcoeff((sum(k=0, 2*n, (k+1)*x^k))^n, n^2, x)}
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Dec 13 2018
STATUS
approved