OFFSET
0,2
MATHEMATICA
a[n_] := Sum[If[n == n - k == 0, 1, (-n)^(n-k)] * Binomial[2*k, k] * Binomial[2*n+1, 2*k], {k, 0, n}]; Array[a, 20, 0] (* Amiram Eldar, Apr 29 2021 *)
PROG
(PARI) {a(n) = sum(k=0, n, (-n)^(n-k)*binomial(2*k, k)*binomial(2*n+1, 2*k))}
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Aug 28 2020
STATUS
approved