OFFSET
0,3
LINKS
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 612
FORMULA
E.g.f.: x^2/((1-x)*(1-2*x)).
D-finite Recurrence: {a(1)=0, a(0)=0, a(2)=2, (2*n^2+6*n+4)*a(n)+(-6-3*n)*a(n+1)+a(n+2)}
a(n) = n!*A000225(n-1). - R. J. Mathar, Jun 03 2022
MAPLE
spec := [S, {S=Prod(Z, Z, Sequence(Z), Sequence(Union(Z, Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
MATHEMATICA
Join[{0}, Table[(2^(n-1)-1)n!, {n, 20}]] (* or *) With[{nn=20}, CoefficientList[ Series[x^2/((1-x)(1-2x)), {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Aug 29 2021 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
STATUS
approved