%I A052663
%S A052663 0,0,0,0,24,240,720,5040,40320,362880,3628800,39916800,479001600,
%T A052663 6227020800,87178291200,1307674368000,20922789888000,355687428096000,
%U A052663 6402373705728000,121645100408832000,2432902008176640000
%N A052663 A simple regular expression in a labeled universe.
%H A052663 INRIA Algorithms Project, <a href="http://algo.inria.fr/bin/encyclopedia?Search=ECSnb&argsearch=610">
               Encyclopedia of Combinatorial Structures 610</a>
%F A052663 E.g.f.: x^4*(-x+x^2-1)/(-1+x)
%F A052663 Recurrence: {a(1)=0, a(0)=0, a(2)=0, (-1-n)*a(n)+a(n+1), a(3)=0, a(4)=24, 
               a(6)=720, a(5)=240}
%F A052663 n! for n >= 4.
%p A052663 spec := [S,{S=Prod(Z,Z,Z,Z,Union(Z,Sequence(Z)))},labeled]: seq(combstruct[count](spec,
               size=n), n=0..20);
%Y A052663 Sequence in context: A003272 A003245 A006863 this_sequence A167548 A052796 
               A056269
%Y A052663 Adjacent sequences: A052660 A052661 A052662 this_sequence A052664 A052665 
               A052666
%K A052663 easy,nonn
%O A052663 0,5
%A A052663 encyclopedia(AT)pommard.inria.fr, Jan 25 2000