OFFSET
0,4
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..449
FORMULA
a(n) = n * a(n-1) - a(n-2) + n * a(n-3) for n > 2.
a(n) ~ n! * (1 - 1/n^2 - 1/n^3 + 5/n^5 + 23/n^6 + 74/n^7 + 161/n^8 - 57/n^9 - 3466/n^10 - ...), for coefficients see A121868. - Vaclav Kotesovec, Nov 25 2022
PROG
(PARI) a(n) = sum(k=0, n\2, (-1)^k*(n-2*k)!);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Nov 23 2022
STATUS
approved