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A027851 Number of nonisomorphic semigroups of order n. 20
1, 1, 5, 24, 188, 1915, 28634, 1627672, 3684030417, 105978177936292 (list; graph; refs; listen; history; text; internal format)



Table of n, a(n) for n=0..9.

Peter Cameron's Blog, The combinatorial explosion, Posted 18/02/2016.

Andreas Distler, Classification and Enumeration of Finite Semigroups, A Thesis Submitted for the Degree of PhD, University of St Andrews (2010).

A. Distler and T. Kelsey, The semigroups of order 9 and their automorphism groups, arXiv preprint arXiv:1301.6023 [math.CO], 2013.

C. Noebauer, Home page

C. Noebauer, The Numbers of Small Rings

C. Noebauer, Thesis on the enumeration of near-rings

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

Jeremy G. Sumner, Michael D. Woodhams, Lie-Markov models derived from finite semigroups, arXiv:1709.00520 [math.GR], 2017.

A. de Vries, Formal Languages: An Introduction, 2012.

Eric Weisstein's World of Mathematics, Semigroup.

Index entries for sequences related to semigroups


a(n) = A001423(n)*2 - A029851(n).

a(n) + A079173(n) = A001329(n).


Cf. A001426, A023814, A058108.

Cf. A001423, A029851, A079173, A001329.

Sequence in context: A009601 A009676 A192995 * A120765 A259355 A297664

Adjacent sequences:  A027848 A027849 A027850 * A027852 A027853 A027854




Christian G. Bower, Dec 13 1997, updated Feb 19 2001


a(8)-a(9) from Andreas Distler, Jan 13 2011



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Last modified January 19 11:41 EST 2019. Contains 319306 sequences. (Running on oeis4.)