OFFSET
0,3
FORMULA
a(n) = n! * Sum_{k=0..floor(n/2)} (n - 2*k)^k/(2^k * k!).
a(n) ~ n! / ((1 + LambertW(1)) * LambertW(1)^(n/2)). - Vaclav Kotesovec, Nov 13 2022
PROG
(PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace(1/(1-x*exp(x^2/2))))
(PARI) a(n) = n!*sum(k=0, n\2, (n-2*k)^k/(2^k*k!));
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Nov 06 2022
STATUS
approved