%I #15 Jun 11 2022 05:22:45
%S 0,0,0,6,72,1080,19440,408240,9797760,264539520,7936185600,
%T 261894124800,9428188492800,367699351219200,15443372751206400,
%U 694951773804288000,33357685142605824000,1701241942272897024000
%N Expansion of e.g.f. x^3/(1-3*x).
%H G. C. Greubel, <a href="/A052678/b052678.txt">Table of n, a(n) for n = 0..350</a>
%H INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=626">Encyclopedia of Combinatorial Structures 626</a>
%F E.g.f.: x^3/(1 - 3*x).
%F Recurrence: a(0)=0, a(1)=0, a(2)=0, a(3)=6, a(n) = 3*n*a(n-1).
%F a(n) = 3^(n-3)*n!, n>2.
%p spec := [S,{S=Prod(Z,Z,Z,Sequence(Union(Z,Z,Z)))},labeled]: seq(combstruct[count](spec,size=n), n=0..20);
%t Table[If[n<3, 0, 3^(n-3)*n!], {n,0,30}] (* _G. C. Greubel_, Jun 11 2022 *)
%o (SageMath) [0,0,0]+[3^(n-3)*factorial(n) for n in (3..30)] # _G. C. Greubel_, Jun 11 2022
%Y Cf. A000142, A000244.
%K easy,nonn
%O 0,4
%A encyclopedia(AT)pommard.inria.fr, Jan 25 2000