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%I #18 Apr 18 2017 07:03:55
%S 1,1,4,30,240,2520,32400,478800,8104320,154586880,3273177600,
%T 76241088000,1937561472000,53340660172800,1581414202368000,
%U 50234310846720000,1702089880178688000,61276407362666496000
%N E.g.f. (1-x)/(1-2x-x^3+x^4).
%H INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=549">Encyclopedia of Combinatorial Structures 549</a>
%F E.g.f.: -(-1+x)/(1-2*x-x^3+x^4)
%F Recurrence: {a(1)=1, a(0)=1, a(2)=4, (n^4+35*n^2+50*n+24+10*n^3)*a(n)+(-n^3-9*n^2-26*n-24)*a(n+1)+(-2*n-8)*a(n+3)+a(n+4)=0, a(3)=30}
%F Sum(-1/643*(-94-127*_alpha-22*_alpha^2+75*_alpha^3)*_alpha^(-1-n), _alpha=RootOf(1-2*_Z-_Z^3+_Z^4))*n!
%F a(n)= n!*A052540(n). - _R. J. Mathar_, Nov 27 2011
%p spec := [S,{S=Sequence(Prod(Z,Union(Sequence(Z),Prod(Z,Z))))},labeled]: seq(combstruct[count](spec,size=n), n=0..20);
%t With[{nn=20},CoefficientList[Series[(1-x)/(1-2x-x^3+x^4),{x,0,nn}],x] Range[0,nn]!] (* _Harvey P. Dale_, Nov 02 2015 *)
%K easy,nonn
%O 0,3
%A encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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