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Search: id:A059443
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| A059443 |
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Triangle T(n,k) (n >= 2) giving number of bicoverings of an n-set with k blocks. |
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33
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| 1, 4, 4, 13, 39, 25, 3, 40, 280, 472, 256, 40, 121, 1815, 6185, 7255, 3306, 535, 15, 364, 11284, 70700, 149660, 131876, 51640, 8456, 420, 1093, 68859, 759045, 2681063, 3961356, 2771685, 954213, 154637, 973, 105
(list; graph; listen)
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OFFSET
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2,2
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COMMENT
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The rows seem to have irregular lengths.
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REFERENCES
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L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 303, #40.
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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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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EXAMPLE
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[1], [4, 4], [13, 39, 25, 3], [40, 280, 472, 256, 40], [121, 1815, 6185, 7255, 3306, 535, 15], [364, 11284, 70700, 149660, 131876, 51640, 8456, 420], [1093, 68859, 759045, 2681063, 3961356, 2771685, 954213, 154637, 9730, 105], ...
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CROSSREFS
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Leading diagonal is A003462. Row sums are A002718. Cf. A059945-A059950.
Sequence in context: A005301 A099924 A019081 this_sequence A097335 A117187 A138767
Adjacent sequences: A059440 A059441 A059442 this_sequence A059444 A059445 A059446
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KEYWORD
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tabf,nonn,nice
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AUTHOR
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njas, Feb 01 2001
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EXTENSIONS
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More terms and additional comments from Vladeta Jovovic (vladeta(AT)Eunet.yu), Feb 14 2001
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