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Search: id:A059950
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| A059950 |
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Number of 9-block bicoverings of an n-set. |
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+0
4
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| 0, 0, 0, 0, 0, 15, 8456, 954213, 66253552, 3622342095, 172672602432, 7557346901841, 312733696544984, 12456923582109435, 483124650731622328, 18383758048494864909, 689931203330381971296, 25630900118611348761735
(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)=(1/9!)*(36^n-9*28^n-36*22^n+72*21^n+252*16^n-336*15^n+378*12^n-1512*11^n+1260*10^n-1890*8^n+5040*7^n-4536*6^n+7560*5^n-8820*4^n-11256*3^n+28728*2^n-19152). 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-A059949, A059951.
Adjacent sequences: A059947 A059948 A059949 this_sequence A059951 A059952 A059953
Sequence in context: A066968 A113795 A074488 this_sequence A140285 A112614 A068732
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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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