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%I #13 Jun 03 2022 18:41:17
%S 1,4,34,432,7320,155040,3940560,116847360,3959786880,150965337600,
%T 6394994323200,297985937356800,15147464243788800,834153946904678400,
%U 49469459519031552000,3143339899991875584000,213046423884047609856000
%N E.g.f. 1/(1-4x-x^2).
%H INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=576">Encyclopedia of Combinatorial Structures 576</a>
%F E.g.f.: -1/(-1+4*x+x^2)
%F Recurrence: {a(0)=1, a(1)=4, (-2-n^2-3*n)*a(n)+(-4*n-8)*a(n+1)+a(n+2)=0}
%F Sum(1/10*(2+_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+4*_Z+_Z^2))*n!
%F a(n)=n!*A001076(n+1). - _R. J. Mathar_, Jun 03 2022
%p spec := [S,{S=Sequence(Union(Z,Z,Z,Z,Prod(Z,Z)))},labeled]: seq(combstruct[count](spec,size=n), n=0..20);
%K easy,nonn
%O 0,2
%A encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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