A007903 The number of distinct principal ideals in the semigroup of binary relations on an n-set.
2, 4, 11, 60, 877, 42944, 7339704
Offset: 1
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.
- Wikipedia, Green's relations
- Index entries for sequences related to semigroups
Crossrefs
Cf. A173311.
Formula
a(n) is asymptotic to 2^(n^2)/n!^2 (from Kim reference). - Geoffrey Critzer, May 14 2023
Comments