OFFSET
0,5
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..350
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 631
FORMULA
E.g.f.: 2*x^4/(1-x)
D-finite recurrence: a(n)=0, a(1)=0, a(2)=0, a(3)=0, a(4)=48, a(n) = n*a(n-1).
a(n) = 2*n!, n>3.
G.f.: 48*x^4*hypergeometric2F0([1,5], [], x). - G. C. Greubel, Jun 04 2022
MAPLE
spec := [S, {S=Prod(Z, Z, Z, Sequence(Z), Union(Z, Z))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
MATHEMATICA
With[{nn=20}, CoefficientList[Series[(2x^4)/(1-x), {x, 0, nn}], x] Range[ 0, nn]!] (* Harvey P. Dale, May 22 2012 *)
Table[2*n!*(1-Boole[n<4]), {n, 0, 40}] (* G. C. Greubel, Jun 04 2022 *)
PROG
(Magma) [n le 3 select 0 else 2*Factorial(n): n in [0..40]]; // G. C. Greubel, Jun 04 2022
(SageMath) [2*factorial(n)*(1 - bool(n<4)) for n in (0..40)] # G. C. Greubel, Jun 04 2022
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
STATUS
approved