OFFSET
0,2
LINKS
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 535
FORMULA
E.g.f.: -(-1+x)/(1-4*x+2*x^2)
Recurrence: {a(0)=1, a(1)=3, (2*n^2+6*n+4)*a(n)+(-4*n-8)*a(n+1)+a(n+2)=0}
Sum(1/4*_alpha^(-1-n), _alpha=RootOf(1-4*_Z+2*_Z^2))*n!
a(n) =n!*A007052(n). - R. J. Mathar, Nov 27 2011
MAPLE
spec := [S, {S=Sequence(Union(Z, Z, Prod(Z, Sequence(Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
MATHEMATICA
With[{nn=20}, CoefficientList[Series[(1-x)/(1-4x+2x^2), {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Jan 10 2014 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
STATUS
approved