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A035347
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Triangle of a(n,k) = number of minimal covers of an n-set that cover k points of that set uniquely (n >= 1, k >= 1).
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5
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1, 0, 2, 0, 3, 5, 0, 6, 28, 15, 0, 10, 190, 210, 52, 0, 15, 1340, 3360, 1506, 203, 0, 21, 9065, 60270, 48321, 10871, 877, 0, 28, 57512, 1132880, 1820056, 636300, 80592, 4140, 0, 36, 344316, 21067452, 76834926, 45455676, 8081928, 618939, 21147, 0, 45
(list; table; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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REFERENCES
| Hearne and Wagner, Minimal covers of finite sets, Discr. Math. 5 (1973), 247-251.
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FORMULA
| a(n, k)=C(n, k)*Sum_{j=1..k} S(k, j)*(2^j-j-1)^(n-k), where S(k, j) are Stirling numbers of the second kind.
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EXAMPLE
| 1; 0,2; 0,3,5; 0,6,28,15; ...
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CROSSREFS
| Cf. A056885 for unlabeled case. Row sums give A046165.
Sequence in context: A109921 A139637 A110990 * A094126 A038072 A161481
Adjacent sequences: A035344 A035345 A035346 * A035348 A035349 A035350
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KEYWORD
| nonn,tabl,easy,nice
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| More terms from Vladeta Jovovic (vladeta(AT)eunet.rs), Sep 06 2000
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