%I A052631
%S A052631 0,1,4,30,288,3480,50400,851760,16450560,357436800,8629286400,229162348800,
%T A052631 6638962176000,208362342988800,7042436719718400,255029193619200000,9851119008546816000,
%U A052631 404305986955014144000,17569457946995834880000,805912049524456562688000
%N A052631 n!*Pell(n) (or n!*A000129(n)).
%H A052631 INRIA Algorithms Project, <a href="http://algo.inria.fr/bin/encyclopedia?Search=ECSnb&argsearch=577">
               Encyclopedia of Combinatorial Structures 577</a>
%F A052631 E.g.f.: -x/(-1+2*x+x^2)
%F A052631 Recurrence: {a(1)=1, a(0)=0, (-2-n^2-3*n)*a(n)+(-4-2*n)*a(n+1)+a(n+2)}
%F A052631 Sum(-1/4*(-1+_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+2*_Z+_Z^2))*n!
%p A052631 spec := [S,{S=Prod(Z,Sequence(Union(Z,Z,Prod(Z,Z))))},labeled]: seq(combstruct[count](spec,
               size=n), n=0..20);
%p A052631 with(combstruct):ZL:=[T,{T=Union(Z,Prod(Epsilon,Z,T),Prod(T,Z,Epsilon),
               Prod(T,Z,Z))},labeled]:seq(count(ZL,size=i),i=0..19); - Zerinvary 
               Lajos (zerinvarylajos(AT)yahoo.com), Dec 16 2007
%Y A052631 Sequence in context: A102307 A052658 A127130 this_sequence A167139 A054972 
               A052452
%Y A052631 Adjacent sequences: A052628 A052629 A052630 this_sequence A052632 A052633 
               A052634
%K A052631 easy,nonn
%O A052631 0,3
%A A052631 encyclopedia(AT)pommard.inria.fr, Jan 25 2000