2,1

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.

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

Index entries for sequences related to semigroups

Column 2 of A058123.

Adjacent sequences: A002784 A002785 A002786 this_sequence A002788 A002789 A002790

Sequence in context: A042465 A041051 A047066 this_sequence A062394 A063766 A020040

nonn

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