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A094545 Number of minimal T_0-covers of an n-set. 3
1, 1, 1, 4, 17, 176, 2287, 49540, 1518337, 67457584, 4254836111, 376795261844, 46709151254449, 8061849904932136, 1936383997541071639, 646603398091877815516, 300476951799493029958913 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,4
COMMENTS
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.
Row sums of A094544.
LINKS
Goran Kilibarda and Vladeta Jovovic, Enumeration of some classes of T_0-hypergraphs, arXiv:1411.4187 [math.CO], 2014.
Eric Weisstein's World of Mathematics, Minimal Cover.
FORMULA
a(n) = Sum_{m=0..n} (n!/m!)*binomial(2^m-m-1, n-m).
a(n) = Sum_{m=0..n} Stirling1(n, m)*A046165(m).
E.g.f.: Sum_{n>=0) x^n*(1+x)^(2^n-n-1)/n!.
CROSSREFS
Sequence in context: A063857 A362646 A072654 * A156633 A032073 A032083
KEYWORD
easy,nonn
AUTHOR
Goran Kilibarda and Vladeta Jovovic, May 08 2004
STATUS
approved

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Last modified June 22 05:36 EDT 2024. Contains 373565 sequences. (Running on oeis4.)