OFFSET
0,3
LINKS
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 691
FORMULA
D-finite with recurrence: a(1)=0; a(2)=2; (-3*n^2+3)*a(n)+(-1-2*n)*a(n+1)+a(n+2) = 0.
MAPLE
spec := [S, {C=Prod(B, S), B=Union(S, Z, C), S=Prod(B, 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