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A070968
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Number of cycles in the bipartite graph K(n,n).
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1
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0, 1, 15, 204, 3940, 113865, 4662231, 256485040, 18226108944, 1623855701385, 177195820499335, 23237493232953516, 3605437233380095620, 653193551573628900289, 136634950180317224866335
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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FORMULA
| a(n) = sum k=2..n C(n, k)^2 * k! * (k-1)! / 2.
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MATHEMATICA
| Table[ Sum[ Binomial[n, k]^2*k!*(k - 1)!, {k, 2, n}]/2, {n, 1, 17}]
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PROG
| (PARI) for(n=1, 50, print1(sum(k=2, n, binomial(n, k)^2 * k! * (k-1)!/2), ", "))
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CROSSREFS
| Cf. A002807, A068087.
Sequence in context: A002007 A178507 A012566 * A075280 A093747 A061637
Adjacent sequences: A070965 A070966 A070967 * A070969 A070970 A070971
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KEYWORD
| nonn
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AUTHOR
| Sharon Sela (sharonsela(AT)hotmail.com), May 17 2002
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EXTENSIONS
| More terms from Benoit Cloitre (benoit7848c(AT)orange.fr) and Robert G. Wilson v (rgwv(AT)rgwv.com), May 20 2002
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