OFFSET
0,1
LINKS
Harvey P. Dale, Table of n, a(n) for n = 0..417
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 608
FORMULA
E.g.f.: -(-2+3*x)/(-1+x+x^2)/(-1+x)
Recurrence: {a(1)=1, a(2)=4, a(0)=2, (n^3+6*n^2+11*n+6)*a(n)+(-2*n-6)*a(n+2)+a(n+3)=0}
(1+Sum(1/5*(-1+3*_alpha)*_alpha^(-1-n), _alpha =RootOf(-1+_Z+_Z^2)))*n!
a(n) = n!*A001611(n-1), n>0. - R. J. Mathar, Nov 27 2011
MAPLE
spec := [S, {S=Union(Sequence(Z), Sequence(Prod(Z, Z, Sequence(Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
MATHEMATICA
With[{nn=20}, CoefficientList[Series[(2-3x)/((1-x)(1-x-x^2)), {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Nov 25 2023 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
STATUS
approved