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A007903 The number of distinct principal ideals in the semigroup of binary relations on an n-set. 0
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

George Markowsky, 1991; Markowsky and Breen, 1993; Breen, 1995.

LINKS

Table of n, a(n) for n=1..7.

Jin Bai Kim, Tables of d-classes in the semigroup Bn1 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

Sequence in context: A091233 A173312 A156434 * A182100 A006894 A193565

Adjacent sequences:  A007900 A007901 A007902 * A007904 A007905 A007906

KEYWORD

nonn,hard,more,nice

AUTHOR

Michael A Breen [ MAB1699(AT)tntech.edu ]

STATUS

approved

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Last modified October 22 12:45 EDT 2018. Contains 316458 sequences. (Running on oeis4.)