%I A052557
%S A052557 1,0,0,6,24,120,1440,15120,161280,2177280,32659200,518918400,
%T A052557 9101030400,174356582400,3574309939200,78460462080000,
%U A052557 1841205510144000,45883678224384000,1210048630382592000
%N A052557 A simple regular expression in a labeled universe.
%H A052557 INRIA Algorithms Project, <a href="http://algo.inria.fr/bin/encyclopedia?Search=ECSnb&argsearch=499">
               Encyclopedia of Combinatorial Structures 499</a>
%F A052557 E.g.f.: (-1+x)/(-1+x+x^3)
%F A052557 Recurrence: {a(1)=0, a(0)=1, a(2)=0, (-11*n-6-n^3-6*n^2)*a(n)+(-n-3)*a(n+2)+a(n+3)}
%F A052557 Sum(-1/31*(2+3*_alpha^2-11*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+_Z+_Z^3))*n!
%p A052557 spec := [S,{S=Sequence(Prod(Z,Z,Z,Sequence(Z)))},labeled]: seq(combstruct[count](spec,
               size=n), n=0..20);
%Y A052557 Sequence in context: A050212 A047865 A060249 this_sequence A052170 A027224 
               A110707
%Y A052557 Adjacent sequences: A052554 A052555 A052556 this_sequence A052558 A052559 
               A052560
%K A052557 easy,nonn
%O A052557 0,4
%A A052557 encyclopedia(AT)pommard.inria.fr, Jan 25 2000