A354279 - OEIS

A354279

Number of regular elements in the semigroup of all binary relations on [n].

1, 2, 16, 470, 40408, 8683982

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OFFSET

0,2

COMMENTS

Let S be a semigroup. An element A in S is regular iff A = A*B*A for some B in S. An element in the semigroup of all binary relations is regular iff its row space forms a distributive lattice under set inclusion.

LINKS

Table of n, a(n) for n=0..5.

K. K.-H. Butler and G. Markowsky, The Number of Maximal Subgroups of the Semigroup of Binary Relations, Kyungpook Math. J. Vol 12, June 1972.

CROSSREFS

Cf. A003425.

Sequence in context: A223563 A140309 A201383 * A306816 A012461 A012458

Adjacent sequences: A354276 A354277 A354278 * A354280 A354281 A354282

KEYWORD

nonn,more

AUTHOR

Geoffrey Critzer, May 22 2022

STATUS

approved