OFFSET
0,5
LINKS
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 681
FORMULA
E.g.f.: RootOf(-_Z+_Z^4+_Z^2+x)-RootOf(-_Z+_Z^4+_Z^2+x)^2-x
D-finite Recurrence: {a(1)=0, a(2)=0, a(3)=0, a(4)=24, a(5)=480, a(6)=10080, (-32256*n^3+85248*n^2-73728*n^5+2304*n-4608-184320*n^4)*a(n) +(-41472*n^3-241344*n^2-92736-289440*n+9216*n^4)*a(n+1) +(-59520*n^2-34048*n^3+79800+56512*n)*a(n+2) +(-7456*n^2-46176*n-61988)*a(n+3) +(-572+2228*n)*a(n+4) +217*a(n+5) =0.
a(n) = n!*A052710(n). - R. J. Mathar, Oct 18 2013
MAPLE
spec := [S, {B=Prod(C, C), C=Union(B, S, Z), S=Prod(B, B)}, 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