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Search: id:A059949
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| A059949 |
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Number of 8-block bicoverings of an n-set. |
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+0
3
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| 0, 0, 0, 0, 0, 535, 51640, 2771685, 114713760, 4127125695, 136631722920, 4292250804985, 130278290187760, 3863262740532195, 112733098867629240, 3252644718804860925, 93093809127731630400, 2649006256251644780935
(list; graph; listen)
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OFFSET
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1,6
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REFERENCES
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I. P. Goulden and D. M. Jackson, Combinatorial Enumeration, John Wiley and Sons, N.Y., 1983.
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FORMULA
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a(n)=(1/8!)*(28^n-8*21^n-28*16^n+56*15^n+168*11^n-224*10^n+210*8^n-840*7^n+700*6^n-840*5^n+1925*4^n+1064*3^n-5460*2^n+4368). E.g.f. for m-block bicoverings of an n-set is exp(-x-1/2*x^2*(exp(y)-1))*Sum_{i=0..inf} x^i/i!*exp(binomial(i, 2)*y).
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CROSSREFS
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Cf. A002718, A059443, A003462, A059945-A059948, A059950-A059951.
Adjacent sequences: A059946 A059947 A059948 this_sequence A059950 A059951 A059952
Sequence in context: A077085 A165989 A067723 this_sequence A077076 A033916 A111258
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KEYWORD
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easy,nonn
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AUTHOR
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Vladeta Jovovic (vladeta(AT)eunet.rs), Feb 14 2001
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