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%I #14 Apr 18 2017 07:04:03
%S 0,0,0,0,24,240,3600,70560,1693440,47900160,1556755200,57081024000,
%T 2328905779200,104589041356800,5124863026483200,272011960636416000,
%U 15543540607795200000,951264685197066240000,62070020709108572160000
%N E.g.f.: (1-2x-sqrt(1-4*x))*x^2/2
%C Apart from a(3) the same as A052733. - _R. J. Mathar_, Oct 16 2013
%H INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=688">Encyclopedia of Combinatorial Structures 688</a>
%F Recurrence: a(1)=0; a(2)=0; a(3)=0; a(4)=24; (-4*n^2+6*n+10)*a(n)+(n-1)*a(n+1)=0 ; a(5)=240;
%F a(n) = n!*A000108(n-3), n>3. - _R. J. Mathar_, Oct 16 2013
%p spec := [S,{B=Union(Z,C),C=Prod(B,B),S=Prod(Z,Z,C)},labeled]: seq(combstruct[count](spec,size=n), n=0..20);
%K easy,nonn
%O 0,5
%A encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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