OFFSET
0,3
LINKS
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 559
FORMULA
E.g.f.: 1/(-1+x)/(-1+x^4)
Recurrence: {a(1)=1, a(0)=1, a(3)=6, a(2)=2, (-61*n-11*n^3-n^4-30-41*n^2)*a(n) +(-n^2-5*n-6)*a(n+1) +(-n-3)*a(n+2) +a(n+4) -a(n+3)=0}
(Sum(1/16*(2*_alpha+_alpha^2-1)*_alpha^(-1-n), _alpha=RootOf(1+_Z+_Z^2+_Z^3))+1/4*n+5/8)*n!
n!*[n/4+1].
a(n)=n!*A008621(n). - R. J. Mathar, Jun 03 2022
MAPLE
spec := [S, {S=Prod(Sequence(Z), Sequence(Prod(Z, Z, Z, Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
MATHEMATICA
With[{nn=20}, CoefficientList[Series[1/((1-x)(1-x^4)), {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Jul 30 2013 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
STATUS
approved