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A383120

a(n) = Sum_{k=0..n} binomial(n,k) * binomial(n*k,k).

1, 2, 11, 139, 2885, 82381, 2979565, 130203494, 6664589321, 390857822425, 25832193906761, 1899273577364197, 153741850998047053, 13585520026454056279, 1301210398133681268381, 134270617908678099820891, 14849785991790603714043921, 1752283118795349858851381297

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OFFSET

0,2

LINKS

Table of n, a(n) for n=0..17.

FORMULA

a(n) = [x^n] ((1 + x)^n + x)^n.

a(n) ~ exp(n + exp(-1) - 1/2) * n^n / sqrt(2*Pi*n). - Vaclav Kotesovec, Apr 17 2025

MATHEMATICA

Table[Sum[Binomial[n, k] Binomial[n k, k], {k, 0, n}], {n, 0, 17}]

PROG

(PARI) a(n) = sum(k=0, n, binomial(n, k) * binomial(n*k, k)); \\ Michel Marcus, Apr 17 2025