OFFSET
0,2
LINKS
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 601
FORMULA
E.g.f.: 1/(-1+x)/(-1+4*x)
Recurrence: {a(0)=1, a(1)=5, (4*n^2+12*n+8)*a(n)+(-10-5*n)*a(n+1)+a(n+2)=0}
(-1/3+1/3*4^(n+1))*n!
a(n) = n!*A002450(n+1). - R. J. Mathar, Nov 27 2011
MAPLE
spec := [S, {S=Prod(Sequence(Z), Sequence(Union(Z, Z, Z, Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
MATHEMATICA
With[{nn=20}, CoefficientList[Series[1/((1-x)(1-4x)), {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Mar 13 2015 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
STATUS
approved