OFFSET
0,1
LINKS
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 572
FORMULA
E.g.f.: -(-3+5*x)/(-1+2*x)/(-1+x)
Recurrence: {a(0)=3, a(1)=4, (2*n^2+6*n+4)*a(n)+(-6-3*n)*a(n+1)+a(n+2)=0}
(2^n+2)*n!
MAPLE
spec := [S, {S=Union(Sequence(Z), Sequence(Z), Sequence(Union(Z, 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