1,2

H. Juergensen and P. Wick, Die Halbgruppen von Ordnungen <= 7, Semigroup Forum, 14 (1977), 69-79.

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

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

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

Index entries for sequences related to semigroups

Column 1 of A058123.

Sequence in context: A089126 A113346 A054926 this_sequence A039719 A014466 A108799

Adjacent sequences: A002783 A002784 A002785 this_sequence A002787 A002788 A002789

nonn,nice,hard

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