A122801 Number of labeled bipartite graphs on 2n vertices having equal parts and no isolated vertices.

1, 1, 21, 2650, 1452605, 3149738046, 26503552820514, 868081172737564500, 111606080497500509325405, 56762846667123360827351083510, 114847831981827229530824587617895286, 927685362544629192461621864598358779955500, 29976424929810726580224613882836823991388901138994

Offset

0,3

Links

Andrew Howroyd, Table of n, a(n) for n = 0..50

Formula

For n>0, a(n) = A001700(n-1) * A048291(n) = A052332(2n) - A122802(2n).

Prog

(PARI) { A122801(n) = binomial(2*n-1, n) * sum(k=0, n, binomial(n, k) * (-1)^k * (2^(n-k)-1)^n ); }

Crossrefs

Cf. A122802, A048291, A052332, A001831, A002031, A047863, A001700.

Sequence in context: A131314 A225686 A221779 * A099680 A352086 A184367

Adjacent sequences: A122798 A122799 A122800 * A122802 A122803 A122804

Keyword

nonn

Author

Max Alekseyev, Sep 11 2006

Extensions

Terms a(11) and beyond from Andrew Howroyd, Nov 07 2019

Status

approved