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A007903 The number of distinct principal ideals in the semigroup of binary relations on an n-set. 1
2, 4, 11, 60, 877, 42944, 7339704 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
a(n) is the number of Green's J-classes in the semigroup of binary relations on an n-set. - James Mitchell, May 10 2015
REFERENCES
K. H. Kim, Boolean Matrix Theory and Applications, Marcel Decker Inc., 1982.
George Markowsky, 1991; Markowsky and Breen, 1993; Breen, 1995.
LINKS
Jin Bai Kim, Tables of D-classes in the semigroup Bn of the binary relations on a set X with n-elements, Bull. Korean Math. Soc., Volume 20, Issue 1, 1983, pp. 9-13.
FORMULA
a(n) is asymptotic to 2^(n^2)/n!^2 (from Kim reference). - Geoffrey Critzer, May 14 2023
CROSSREFS
Cf. A173311.
Sequence in context: A173312 A351184 A156434 * A182100 A327484 A006894
KEYWORD
nonn,hard,more,nice
AUTHOR
Michael A Breen (MAB1699(AT)tntech.edu)
STATUS
approved

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Last modified May 20 05:07 EDT 2024. Contains 372703 sequences. (Running on oeis4.)