OFFSET
0,2
FORMULA
a(n) ~ sqrt(Pi) * n^(n^2/2 + 1) / (2^(n^2/2 + 1/2) * exp(n^2/4)) if n is even, and a(n) ~ sqrt(Pi) * n^(n^2/2 + 1/2) / (2^(n^2/2 - 1) * exp(n^2/4)) if n is odd.
MATHEMATICA
Table[Sum[(k*(n-k))!, {k, 0, n}], {n, 0, 14}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Vaclav Kotesovec, Feb 03 2018
STATUS
approved