0,3

G. E. Forsythe, SWAC computes 126 distinct semigroups of order 4, Proc. Amer. Math. Soc. 6, (1955). 443-447.

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

D. J. Kleitman, B. L. Rothschild and J. H. Spencer, The number of semigroups of order n, Proc. Amer. Math. Soc., 55 (1976), 227-232.

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

Satoh, S.; Yama, K.; and Tokizawa, M., Semigroups of order 8, Semigroup Forum 49 (1994), 7-29.

Eric Postpischil Posting to sci.math newsgroup, May 21 1990

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

Index entries for sequences related to semigroups

a(n)=(A027851(n)+A029851(n))/2. Cf. A001426, A023814, A058107, A058123.

Adjacent sequences: A001420 A001421 A001422 this_sequence A001424 A001425 A001426

Sequence in context: A112294 A073511 A108704 this_sequence A034517 A065857 A060841

nonn,hard,nice

njas