OFFSET
0,3
LINKS
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 807
FORMULA
E.g.f.: log((-1+x)/(-1+2*x))*x.
D-finite with recurrence: {a(1)=0, a(2)=2, (-2*n+2*n^3-4+4*n^2)*a(n)+(-6*n-3*n^2)*a(n+1)+(n+1)*a(n+2)}.
For n > 1, a(n) = n! * (2^(n-1) - 1)/(n-1). - Vaclav Kotesovec, Jun 06 2019
MAPLE
spec := [S, {B=Sequence(Z, 1 <= card), C=Cycle(B), S=Prod(Z, C)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
MATHEMATICA
Flatten[{0, 0, Table[n!*(2^(n-1) - 1)/(n-1), {n, 2, 20}]}] (* Vaclav Kotesovec, Jun 06 2019 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
STATUS
approved