A366564 Expansion of e.g.f. -log(1 - x^2 * (exp(x) - 1)).
0, 0, 0, 6, 12, 20, 390, 2562, 11816, 166392, 1970730, 17131070, 241009692, 3861669396, 51411143966, 828234487290, 15865154629200, 283329069136112, 5431892804244306, 119420738547382134, 2628980439169097540, 59707303735169923980, 1488953374718002643142
Offset: 0
Keywords
Programs
-
PARI
a(n) = n!*sum(k=1, n\3, (k-1)!*stirling(n-2*k, k, 2)/(n-2*k)!);
Formula
a(n) = n! * Sum_{k=1..floor(n/3)} (k-1)! * Stirling2(n-2*k,k)/(n-2*k)!.