0,3

An idempotent semigroup is one whose elements are all idempotents.

R. J. Plemmons, There are 15973 semigroups of order 6, Math. Algor., 2 (1967), 2-17; 3 (1968), 23.

R. J. Plemmons, Construction and analysis of non-equivalent finite semigroups, pp. 223-228 of J. Leech, editor, Computational Problems in Abstract Algebra. Pergamon, Oxford, 1970.

S. Satoh, K. Yama and M. Tokizawa, Semigroups of order 8; Semigroup Forum 49, 1994.

Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.

Index entries for sequences related to semigroups

Cf. A001423. Main diagonal of A058123.

Adjacent sequences: A002785 A002786 A002787 this_sequence A002789 A002790 A002791

Sequence in context: A159667 A030957 A030898 this_sequence A134094 A009575 A127116

nonn,nice,hard

N. J. A. Sloane (njas(AT)research.att.com).

Additional reference and comments from Michael Somos.

a(7) term from Christian G. Bower (bowerc(AT)usa.net), Feb 19 2001

a(8) (from the Satoh et al. reference) sent by Tom Kelsey (tom(AT)cs.st-and.ac.uk), Jun 17 2008