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%I #18 Sep 06 2020 13:20:26
%S 1,0,4,12,144,1200,15840,211680,3467520,61689600,1241049600,
%T 27223257600,654316185600,16999766784000,476167826534400,
%U 14282419447296000,457079267893248000,15539983733514240000
%N E.g.f. (1-x)/(1-x-2x^2).
%H INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=543">Encyclopedia of Combinatorial Structures 543</a>
%F E.g.f.: (-1+x)/(-1+x+2*x^2)
%F Recurrence: {a(1)=0, a(0)=1, (-2*n^2-6*n-4)*a(n)+(-2-n)*a(n+1)+a(n+2)=0}
%F Sum(1/9*(-1+5*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+_Z+2*_Z^2))*n!
%F a(n) = n!*A078008(n). - _R. J. Mathar_, Nov 27 2011
%p spec := [S,{S=Sequence(Prod(Z,Sequence(Z),Union(Z,Z)))},labeled]: seq(combstruct[count](spec,size=n), n=0..20);
%t With[{nn=20},CoefficientList[Series[(1-x)/(1-x-2x^2),{x,0,nn}],x] Range[ 0,nn]!] (* _Harvey P. Dale_, Sep 06 2020 *)
%K easy,nonn
%O 0,3
%A encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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