OFFSET
0,3
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..449
FORMULA
a(n) = n!*hypergeom([-floor(n/2)], [-floor(n/2)], 1).
a(n) = n!*Sum_{k=0..floor(n/2)} 1/k!. - Seiichi Manyama, Jul 17 2022
D-finite with recurrence a(n) -n*a(n-1) +2*(-n+1)*a(n-2) +2*(n-1)*(n-2)*a(n-3)=0. - R. J. Mathar, Jul 27 2022
a(n) ~ exp(1) * n!. - Vaclav Kotesovec, Feb 28 2024
MAPLE
egf := -exp(x^2)/(x - 1): ser := series(egf, x, 26):
seq(n!*coeff(ser, x, n), n = 0..22);
PROG
(PARI) a(n) = n!*sum(k=0, n\2, 1/k!); \\ Seiichi Manyama, Jul 17 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Peter Luschny, Jul 15 2022
STATUS
approved