OFFSET
0,4
LINKS
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 700
FORMULA
D-finite with recurrence: a(1)=0, a(2)=0, a(3)=6, (-4*n^4-24*n-24*n^3-44*n^2)*a(n) +(-8*n^3-42*n^2-12-58*n)*a(n+1) +(-3*n^2-8*n+3)*a(n+2) +(n+2)*a(n+3)=0, a(4)=48, a(5)=840, a(6)=17280.
a(n) ~ sqrt(58-41*sqrt(2))*(1+sqrt(2))^(n-1)*2^n*n^(n-1)*exp(-n). - Vaclav Kotesovec, Aug 18 2013
a(n)= n!*A052705(n-1). - R. J. Mathar, Oct 26 2013
MAPLE
spec := [S, {B=Prod(C, C), S=Prod(B, Z), C=Union(B, S, Z)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
STATUS
approved