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Search: id:A094545
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| A094545 |
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Number of minimal T_0-covers of an n-set. |
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4
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| 1, 1, 1, 4, 17, 176, 2287, 49540, 1518337, 67457584, 4254836111, 376795261844, 46709151254449, 8061849904932136, 1936383997541071639, 646603398091877815516, 300476951799493029958913
(list; table; graph; listen)
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OFFSET
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0,4
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COMMENT
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A cover of a set is a T_0-cover if for every two distinct points of the set there exists a member (block) of the cover containing one but not the other point.
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REFERENCES
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G. Kilibarda and V. Jovovic, "Enumeration of some classes of T_0-hypergraphs", in preparation, 2004.
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LINKS
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Eric Weisstein's World of Mathematics, Minimal Cover.
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FORMULA
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a(n) = Sum(n!/m!*binomial(2^m-m-1, n-m), m=0..n) = Sum(Stirling1(n, m)*A046165(m), m=0..n). E.g.f.: Sum(x^n*(1+x)^(2^n-n-1)/n!, n=0..infinity). Row sums of A094544.
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CROSSREFS
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Cf. A035348, A046165, A094544, A094546.
Sequence in context: A129436 A063857 A072654 this_sequence A032073 A032083 A126776
Adjacent sequences: A094542 A094543 A094544 this_sequence A094546 A094547 A094548
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KEYWORD
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easy,nonn,tabl
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AUTHOR
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Goran Kilibarda, Vladeta Jovovic (vladeta(AT)Eunet.yu), May 08 2004
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