OFFSET
0,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..310
FORMULA
a(n) = Sum_{k=0..n} binomial((n+1)*n,k) * binomial(n^2-k-1,n-k).
From Vaclav Kotesovec, Feb 08 2020: (Start)
a(n) ~ 2^(n - 1/2) * exp(n) * n^(n - 1/2) / sqrt(Pi).
a(n) = binomial(n*(n+1), 2*n) * binomial(2*n, n) / binomial(n*(n+1)/2, n). (End)
MATHEMATICA
Table[Sum[Binomial[(n + 1)*n, k]*Binomial[n^2 - k - 1, n - k], {k, 0, n}], {n, 0, 15}] (* Vaclav Kotesovec, Feb 08 2020 *)
Table[Binomial[n*(n+1), 2*n] * Binomial[2*n, n] / Binomial[n*(n+1)/2, n], {n, 0, 15}] (* Vaclav Kotesovec, Feb 08 2020 *)
PROG
(PARI) {a(n) = sum(k=0, n, binomial((n+1)*n, k)*binomial(n^2-k-1, n-k))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Feb 08 2020
STATUS
approved