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A122801
Number of labeled bipartite graphs on 2n vertices having equal parts and no isolated vertices.
2
1, 1, 21, 2650, 1452605, 3149738046, 26503552820514, 868081172737564500, 111606080497500509325405, 56762846667123360827351083510, 114847831981827229530824587617895286, 927685362544629192461621864598358779955500, 29976424929810726580224613882836823991388901138994
OFFSET
0,3
LINKS
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 ); }
KEYWORD
nonn
AUTHOR
Max Alekseyev, Sep 11 2006
EXTENSIONS
Terms a(11) and beyond from Andrew Howroyd, Nov 07 2019
STATUS
approved