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(2^n+2)*n!.
0

%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