A291547 a(n) = ((2*n-1)!!)^n.

1, 9, 3375, 121550625, 753631499840625, 1261673443947253805015625, 822952789790387281855874669859609375, 285018362247755338974104595257347347998199462890625, 68512882179510153729154120317673085873841328059500855014801025390625

Offset: 1

Author

Vaclav Kotesovec, Aug 26 2017

Keywords

• nonn

Crossrefs

Cf. A001147, A036740, A254866, A291332.

Programs

Mathematica

Table[Product[2*k - 1, {k, 1, n}]^n, {n, 1, 10}]
Table[((2*n - 1)!!)^n, {n, 1, 10}]

Formula

a(n) = ((2*n)!/n!)^n / 2^(n^2).

a(n) ~ 2^(n^2 + n/2) * n^(n^2) / exp(n^2 + 1/24).