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A001426 Number of commutative semigroups of order n.
(Formerly M2929 N1177)
17
1, 1, 3, 12, 58, 325, 2143, 17291, 221805, 11545843, 3518930337 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

REFERENCES

Grillet, P.A., Computing Finite Commutative Semigroups, Semigroup Forum 53 (1996), 140-154.

Grillet, P.A., Computing Finite Commutative Semigroups: Part II, Semigroup Forum 67 (2003), 159-184.

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.

R. J. Plemmons, Cayley Tables for All Semigroups of Order Less Than 7. Department of Mathematics, Auburn Univ., 1965.

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

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).

LINKS

Table of n, a(n) for n=0..10.

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

Eric Weisstein's World of Mathematics, Semigroup.

Index entries for sequences related to semigroups

CROSSREFS

Cf. A001423, A023815, A027851, A058105, A058116.

a(n) + A079193(n) + A079196(n) + A079199(n) = A001329(n).

Sequence in context: A196708 A184511 A125276 * A059440 A020075 A020030

Adjacent sequences:  A001423 A001424 A001425 * A001427 A001428 A001429

KEYWORD

nonn,nice,hard,more

AUTHOR

N. J. A. Sloane.

EXTENSIONS

a(8) (from the Satoh et al. paper) supplied by Richard Schroeppel, Jul 22 2005

a(9) and a(10) from Grillet references sent by Jens Zumbragel (jzumbr(AT)math.unizh.ch), Jun 14 2006

STATUS

approved

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Last modified April 18 19:02 EDT 2014. Contains 240733 sequences.