OFFSET
0,3
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.
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..8
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=n..2^n-1} m!/n!*binomial(2^n-n-1, m-n).
MATHEMATICA
Table[Sum[(m!/n!)*Binomial[2^n - n - 1, m - n], {m, n, 2^n - 1}], {n, 0, 5}] (* G. C. Greubel, Oct 07 2017 *)
PROG
(PARI) for(n=0, 5, print1(sum(m=n, 2^n -1, (m!/n!)*binomial(2^n-n-1, m-n)), ", ")) \\ G. C. Greubel, Oct 07 2017
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Goran Kilibarda and Vladeta Jovovic, May 08 2004
STATUS
approved