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Search: id:A060052
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| A060052 |
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Triangle read by rows: T(n,k) (n >= 2) gives number of r-bicoverings of an n-set with k blocks. |
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4
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| 1, 1, 4, 15, 25, 3, 30, 222, 226, 40, 30, 1230, 3670, 2706, 535, 15, 5040, 39900, 69450, 40405, 8141, 420, 15120, 345240, 1254960, 1498035, 722275, 142877, 9730, 105, 30240, 2492280, 18587520, 40701780, 36450820, 15031204, 2871240, 226828, 5040
(list; table; graph; listen)
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OFFSET
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2,3
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COMMENT
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A bicovering is r-bicovering if intersection of every two blocks contains at most one element.
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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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LINKS
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Table
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FORMULA
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E.g.f. for number of k-block r-bicoverings of an n-set is exp(-x-1/2*x^2*y)*Sum_{i=0..inf} (1+y)^binomial(i, 2)*x^i/i!.
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EXAMPLE
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[1], [1, 4], [15, 25, 3], [30, 222, 226, 40], [30, 1230, 3670, 2706, 535, 15], [5040, 39900, 69450, 40405, 8141, 420], [15120, 345240, 1254960, 1498035, 722275, 142877, 9730, 105], [30240, 2492280, 18587520, 40701780, 36450820, 15031204, 2871240, 226828, 5040], ...
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CROSSREFS
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Cf. A060053(row sums), A060051(column sums), A002718, A059443, A003462, A059945-A059951.
Adjacent sequences: A060049 A060050 A060051 this_sequence A060053 A060054 A060055
Sequence in context: A054308 A051531 A062835 this_sequence A063129 A061873 A017437
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KEYWORD
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easy,nonn,tabl
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AUTHOR
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Vladeta Jovovic (vladeta(AT)Eunet.yu), Feb 15 2001
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