OFFSET
0,5
COMMENTS
Apart from a(3) the same as A052733. - R. J. Mathar, Oct 16 2013
LINKS
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 688
FORMULA
Recurrence: a(1)=0; a(2)=0; a(3)=0; a(4)=24; (-4*n^2+6*n+10)*a(n)+(n-1)*a(n+1)=0 ; a(5)=240;
a(n) = n!*A000108(n-3), n>3. - R. J. Mathar, Oct 16 2013
MAPLE
spec := [S, {B=Union(Z, C), C=Prod(B, B), S=Prod(Z, Z, C)}, 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