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%I #13 Jun 03 2022 18:46:21
%S 1,1,2,18,120,840,9360,115920,1491840,22861440,395539200,7304774400,
%T 148011494400,3281639961600,77850214041600,1975895970048000,
%U 53666956062720000,1547595999645696000,47204701332332544000
%N E.g.f. 1/(1-x-2x^3).
%H INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=555">Encyclopedia of Combinatorial Structures 555</a>
%F E.g.f.: -1/(-1+x+2*x^3)
%F Recurrence: {a(1)=1, a(0)=1, a(2)=2, (-12*n^2-22*n-12-2*n^3)*a(n) +(-n-3)*a(n+2) +a(n+3)=0}
%F Sum(1/29*(2+6*_alpha^2+9*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+_Z+2*_Z^3))*n!
%F a(n)=n!*A077949(n). - _R. J. Mathar_, Jun 03 2022
%p spec := [S,{S=Sequence(Union(Z,Prod(Z,Z,Union(Z,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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