A001426 - OEIS

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A001426

Number of commutative semigroups of order n.
(Formerly M2929 N1177)

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 June 19 01:02 EDT 2013. Contains 226359 sequences.