cp's OEIS Frontend

A052647 E.g.f. (2-2x-x^2)/((1-2x)(1-x^2)).

%I A052647 #13 Apr 18 2017 07:03:58
%S A052647 2,2,10,48,408,3840,46800,645120,10362240,185794560,3719520000,
%T A052647 81749606400,1962469555200,51011754393600,1428416301312000,
%U A052647 42849873690624000,1371216880889856000,46620662575398912000
%N A052647 E.g.f. (2-2x-x^2)/((1-2x)(1-x^2)).
%H A052647 INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=593">Encyclopedia of Combinatorial Structures 593</a>
%F A052647 E.g.f.: -(-2+x^2+2*x)/(-1+2*x)/(-1+x^2)
%F A052647 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 A052647 (2^n+Sum(1/2*_alpha^(-n), _alpha=RootOf(-1+_Z^2)))*n!
%F A052647 n!*[2^n+(n mod 2)].
%F A052647 a(n) = n!*A052531(n). - _R. J. Mathar_, Nov 27 2011
%p A052647 spec := [S,{S=Union(Sequence(Prod(Z,Z)),Sequence(Union(Z,Z)))},labeled]: seq(combstruct[count](spec,size=n), n=0..20);
%K A052647 easy,nonn
%O A052647 0,1
%A A052647 encyclopedia(AT)pommard.inria.fr, Jan 25 2000