OFFSET
0,3
LINKS
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 542
FORMULA
E.g.f.: -1/(-1+x^2+x^3)
Recurrence: {a(1)=0, a(0)=1, a(2)=2, (-11*n-6-n^3-6*n^2)*a(n) +(-n^2-5*n-6)*a(n+1) +a(n+3)=0}
Sum(-1/23*(-3-7*_alpha+2*_alpha^2)*_alpha^(-1-n), _alpha=RootOf(_Z^3+_Z^2-1))*n!
a(n) = n!*A000931(n+3). - R. J. Mathar, Nov 27 2011
MAPLE
spec := [S, {S=Sequence(Prod(Z, Union(Z, Prod(Z, Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
MATHEMATICA
With[{nn=20}, CoefficientList[Series[1/(1-x^2-x^3), {x, 0, nn}], x] Range[ 0, nn]!] (* Harvey P. Dale, Oct 18 2013 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
STATUS
approved