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%I #13 Apr 18 2017 07:03:58
%S 2,2,10,48,408,3840,46800,645120,10362240,185794560,3719520000,
%T 81749606400,1962469555200,51011754393600,1428416301312000,
%U 42849873690624000,1371216880889856000,46620662575398912000
%N E.g.f. (2-2x-x^2)/((1-2x)(1-x^2)).
%H INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=593">Encyclopedia of Combinatorial Structures 593</a>
%F E.g.f.: -(-2+x^2+2*x)/(-1+2*x)/(-1+x^2)
%F Recurrence: {a(1)=2, a(2)=10, a(0)=2, (12+2*n^3+12*n^2+22*n)*a(n)+(-n^2-5*n-6)*a(n+1)+(-2*n-6)*a(n+2)+a(n+3)=0}
%F (2^n+Sum(1/2*_alpha^(-n), _alpha=RootOf(-1+_Z^2)))*n!
%F n!*[2^n+(n mod 2)].
%F a(n) = n!*A052531(n). - _R. J. Mathar_, Nov 27 2011
%p spec := [S,{S=Union(Sequence(Prod(Z,Z)),Sequence(Union(Z,Z)))},labeled]: seq(combstruct[count](spec,size=n), n=0..20);
%K easy,nonn
%O 0,1
%A encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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