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%I #14 Apr 18 2017 07:03:54
%S 0,0,2,6,48,480,5760,80640,1290240,23224320,464486400,10218700800,
%T 245248819200,6376469299200,178541140377600,5356234211328000,
%U 171399494762496000,5827582821924864000,209792981589295104000
%N E.g.f. x^2(1-x)/(1-2x).
%C Essentially the same as A051578. - _R. J. Mathar_, Feb 22 2008
%H INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=532">Encyclopedia of Combinatorial Structures 532</a>
%F E.g.f.: x^2*(-1+x)/(-1+2*x)
%F Recurrence: {a(1)=0, a(0)=0, a(3)=6, a(2)=2, (-2*n-2)*a(n)+a(n+1)=0}
%F 1/8*2^n*n!, n>2.
%p spec := [S,{S=Prod(Z,Z,Sequence(Prod(Z,Sequence(Z))))},labeled]: seq(combstruct[count](spec,size=n), n=0..20);
%K easy,nonn
%O 0,3
%A encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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