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%I #19 Jan 20 2024 16:57:39
%S 0,0,4,18,48,240,1440,10080,80640,725760,7257600,79833600,958003200,
%T 12454041600,174356582400,2615348736000,41845579776000,
%U 711374856192000,12804747411456000,243290200817664000
%N Expansion of e.g.f. x^2*(2+x-x^2)/(1-x).
%H INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=588">Encyclopedia of Combinatorial Structures 588</a>
%F E.g.f.: x^2*(-x+x^2-2)/(-1+x).
%F Recurrence: {a(1)=0, a(0)=0, (-1-n)*a(n)+a(n+1)=0, a(2)=4, a(4)=48, a(3)=18}
%F 2*n!
%F a(n) = A052628(n), n>1. - _R. J. Mathar_, Jan 30 2009
%p spec := [S,{S=Prod(Z,Z,Union(Z,Sequence(Z),Sequence(Z)))},labeled]: seq(combstruct[count](spec,size=n), n=0..20);
%t With[{nn=20},CoefficientList[Series[x^2 (2+x-x^2)/(1-x),{x,0,nn}],x] Range[ 0,nn]!] (* _Harvey P. Dale_, Sep 04 2020 *)
%Y Cf. A052628.
%K easy,nonn
%O 0,3
%A encyclopedia(AT)pommard.inria.fr, Jan 25 2000