OFFSET
0,1
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..360
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 644
FORMULA
E.g.f.: (2-5*x)/((1-x)*(1-4*x)).
D-finite Recurrence: a(0)=2, a(1)=5, a(n) = 5*n*a(n-1) - 4*n*(n-1)*a(n-2).
a(n) = (4^n + 1)*n!.
MAPLE
spec := [S, {S=Union(Sequence(Z), Sequence(Union(Z, Z, Z, Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
MATHEMATICA
With[{nn=20}, CoefficientList[Series[(2-5x)/((1-4x)(1-x)), {x, 0, nn}], x] Range[ 0, nn]!] (* Harvey P. Dale, Sep 12 2020 *)
PROG
(SageMath) [factorial(n)*(4^n +1) for n in (0..30)] # G. C. Greubel, May 31 2022
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
STATUS
approved