OFFSET
0,2
LINKS
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 615
FORMULA
E.g.f.: -1/(-1+2*x+x^4)
Recurrence: {a(0)=1, a(1)=2, a(2)=8, a(3)=48, (-n^4-35*n^2-50*n-24-10*n^3)*a(n)+(-2*n-8)*a(n+3)+a(n+4)=0}
Sum(1/86*(27+18*_alpha^3+12*_alpha^2+8*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+2*_Z+_Z^4))*n!
a(n) = n!*A008999(n). - R. J. Mathar, Nov 27 2011
MAPLE
spec := [S, {S=Sequence(Union(Z, Z, Prod(Z, Z, 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