A001427 - OEIS

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A001427

Number of regular semigroups of order n, considered to be equivalent when they are isomorphic or anti-isomorphic (by reversal of the operator).
(Formerly M2823 N1136)

1, 3, 9, 42, 206, 1352, 10168, 91073, 925044 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,2`
	REFERENCES	`S. Satoh, K. Yama, M. Tokizawa, Semigroups of order 8, Semigroup Forum 49 (1994), 7-29.` `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.` `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	`Andreas Distler, Classification and Enumeration of Finite Semigroups, A Thesis Submitted for the Degree of PhD, University of St Andrews (2010).` `Index entries for sequences related to semigroups`
	CROSSREFS	`Sequence in context: A183306 A057724 A129879 * A020128 A018965 A018995` `Adjacent sequences: A001424 A001425 A001426 * A001428 A001429 A001430`
	KEYWORD	`nonn,nice,hard,more`
	AUTHOR	`N. J. A. Sloane (njas(AT)research.att.com).`
	EXTENSIONS	`a(8) and a(9) from Andreas Distler (andreas(AT)mcs.st-andrews.ac.uk), Jan 17 2011`

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Last modified February 14 18:47 EST 2012. Contains 205663 sequences.