%I A122801
%S A122801 1,1,21,2650,1452605,3149738046,26503552820514,868081172737564500,
%T A122801 111606080497500509325405,56762846667123360827351083510,
%U A122801 114847831981827229530824587617895286
%N A122801 Number of labeled bipartite graphs on 2n vertices having equal parts 
               and no isolated vertices.
%F A122801 For n>0, a(n) = A001700(n-1) * A048291(n) = A052332(2n) - A122802(2n)
%o A122801 (PARI) { a(n) = binomial(2*n-1,n)*sum(k=0, n, binomial(n, k)*(-1)^k*(2^(n-k)-1)^n) 
               }
%Y A122801 Cf. A122802, A048291, A052332, A001831, A002031, A047863, A001700.
%Y A122801 Sequence in context: A068254 A144853 A131314 this_sequence A099680 A114934 
               A098375
%Y A122801 Adjacent sequences: A122798 A122799 A122800 this_sequence A122802 A122803 
               A122804
%K A122801 nonn
%O A122801 0,3
%A A122801 Max Alekseyev (maxale(AT)gmail.com), Sep 11 2006