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Search: id:A059948
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| A059948 |
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Number of 7-block bicoverings of an n-set. |
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+0
3
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| 0, 0, 0, 0, 40, 3306, 131876, 3961356, 103290096, 2488179582, 57162274972, 1274774473632, 27887396866472, 602352276704178, 12899161619186388, 274612697648135028, 5822592730060070368, 123107330974129584294
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OFFSET
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1,5
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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)=(1/7!)*(21^n-7*15^n-21*11^n+42*10^n+105*7^n-140*6^n+105*5^n-420*4^n+35*3^n+1050*2^n-1050). 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-A059947, A059949-A059951.
Sequence in context: A140729 A003741 A049215 this_sequence A045502 A123810 A146198
Adjacent sequences: A059945 A059946 A059947 this_sequence A059949 A059950 A059951
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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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