%I A052700
%S A052700 0,1,4,36,432,6480,116640,2449440,58786560,1587237120,47617113600,
%T A052700 1571364748800,56569130956800,2206196107315200,92660236507238400,
%U A052700 4169710642825728000,200146110855634944000,10207451653637382144000
%N A052700 A simple regular expression in a labeled universe.
%H A052700 INRIA Algorithms Project, <a href="http://algo.inria.fr/bin/encyclopedia?Search=ECSnb&argsearch=650">
               Encyclopedia of Combinatorial Structures 650</a>
%F A052700 E.g.f.: x*(-1+x)/(-1+3*x)
%F A052700 Recurrence: {a(1)=1, a(0)=0, a(2)=4, (-3*n-3)*a(n)+a(n+1)}
%F A052700 2/9*3^n*n!
%p A052700 spec := [S,{S=Prod(Z,Sequence(Prod(Sequence(Z),Union(Z,Z))))},labeled]: 
               seq(combstruct[count](spec,size=n), n=0..20);
%Y A052700 Sequence in context: A002894 A131765 A132864 this_sequence A167540 A136224 
               A009533
%Y A052700 Adjacent sequences: A052697 A052698 A052699 this_sequence A052701 A052702 
               A052703
%K A052700 easy,nonn
%O A052700 0,3
%A A052700 encyclopedia(AT)pommard.inria.fr, Jan 25 2000