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Search: id:A122801
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| A122801 |
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Number of labeled bipartite graphs on 2n vertices having equal parts and no isolated vertices. |
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+0
2
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| 1, 1, 21, 2650, 1452605, 3149738046, 26503552820514, 868081172737564500, 111606080497500509325405, 56762846667123360827351083510, 114847831981827229530824587617895286
(list; graph; listen)
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OFFSET
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0,3
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FORMULA
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For n>0, a(n) = A001700(n-1) * A048291(n) = A052332(2n) - A122802(2n)
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PROGRAM
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(PARI) { a(n) = binomial(2*n-1, n)*sum(k=0, n, binomial(n, k)*(-1)^k*(2^(n-k)-1)^n) }
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CROSSREFS
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Cf. A122802, A048291, A052332, A001831, A002031, A047863, A001700.
Sequence in context: A068254 A144853 A131314 this_sequence A099680 A114934 A098375
Adjacent sequences: A122798 A122799 A122800 this_sequence A122802 A122803 A122804
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KEYWORD
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nonn
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AUTHOR
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Max Alekseyev (maxale(AT)gmail.com), Sep 11 2006
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