A052576 - OEIS

%I #13 Apr 18 2017 07:03:54

%S 1,2,10,48,384,3840,46080,645120,10321920,185794560,3715891200,

%T 81749606400,1961990553600,51011754393600,1428329123020800,

%U 42849873690624000,1371195958099968000,46620662575398912000

%N E.g.f. (1+x^2-2x^3)/(1-2x).

%H INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=519">Encyclopedia of Combinatorial Structures 519</a>

%F E.g.f.: (-x^2+2*x^3-1)/(-1+2*x)

%F Recurrence: {a(0)=1, a(1)=2, (-2*n-2)*a(n)+a(n+1)=0, a(2)=10, a(3)=48}

%F 2^n*n!, n>2.

%p spec := [S,{S=Union(Prod(Z,Z),Sequence(Union(Z,Z)))},labeled]: seq(combstruct[count](spec,size=n), n=0..20);

%Y Essentially the same as A000165 (which is the main entry).

%K easy,nonn

%O 0,2

%A encyclopedia(AT)pommard.inria.fr, Jan 25 2000