%I #11 Apr 18 2017 07:03:57
%S 3,4,12,60,432,4080,47520,655200,10402560,186520320,3723148800,
%T 81829440000,1962948556800,51024208435200,1428503479603200,
%U 42852489039360000,1371237803679744000,46621373950255104000
%N (2^n+2)*n!.
%H INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=572">Encyclopedia of Combinatorial Structures 572</a>
%F E.g.f.: -(-3+5*x)/(-1+2*x)/(-1+x)
%F Recurrence: {a(0)=3, a(1)=4, (2*n^2+6*n+4)*a(n)+(-6-3*n)*a(n+1)+a(n+2)=0}
%F (2^n+2)*n!
%p spec := [S,{S=Union(Sequence(Z),Sequence(Z),Sequence(Union(Z,Z)))},labeled]: seq(combstruct[count](spec,size=n), n=0..20);
%K easy,nonn
%O 0,1
%A encyclopedia(AT)pommard.inria.fr, Jan 25 2000