OFFSET
0,3
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..200
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 605
FORMULA
E.g.f.: (-1+x^2)*(-1+x)/(x^3-x^2-2*x+1)
Recurrence: {a(1)=1, a(0)=1, a(2)=4, (n^3+6*n^2+11*n+6)*a(n)+(-n^2-5*n-6)*a(n+1)+(-2*n-6)*a(n+2)+a(n+3)=0, a(3)=30}
Sum(-1/7*(_alpha+_alpha^2-2)*_alpha^(-1-n), _alpha=RootOf(_Z^3-_Z^2-2*_Z+1))*n!
a(n) = n!*A006054(n+1),n>0. - R. J. Mathar, Jun 03 2022
MAPLE
spec := [S, {S=Sequence(Prod(Z, Sequence(Z), Sequence(Prod(Z, Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
MATHEMATICA
With[{nn=20}, CoefficientList[Series[((1-x^2)(1-x))/(1-2x-x^2+x^3), {x, 0, nn}], x]Range[0, nn]!] Harvey P. Dale, May 16 2012
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
STATUS
approved