A254866 a(n) = (n!!)^n.

1, 1, 4, 27, 4096, 759375, 12230590464, 140710042265625, 472769874482845188096, 601016336033894136931640625, 697127546117424200558837760000000000, 153133225508583375568553948649382367138671875, 91653624689233987245068783089656480594395136000000000000

Offset

0,3

Links

Table of n, a(n) for n=0..12.

Eric Weisstein, Double Factorial, (MathWorld)

Formula

a(n) ~ Pi^(n/2) * n^(n*(n+1)/2) / exp(n^2/2 - 1/6) if n is even.

a(n) ~ 2^(n/2) * n^(n*(n+1)/2) / exp(n^2/2 - 1/6) if n is odd.

Mathematica

Table[(n!!)^n, {n, 0, 15}]

Crossrefs

Cf. A006882, A036740, A185141.

Cf. A000165, A001147.

Sequence in context: A132641 A008973 A132646 * A292968 A000869 A132640

Adjacent sequences: A254863 A254864 A254865 * A254867 A254868 A254869

Keyword

nonn,easy

Author

Vaclav Kotesovec, Feb 19 2015

Status

approved