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A027851 Number of nonisomorphic semigroups of order n. 18
1, 1, 5, 24, 188, 1915, 28634, 1627672, 3684030417, 105978177936292 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

REFERENCES

A. de Vries, Formal Languages: An Introduction, http://haegar.fh-swf.de/Seminare/Genome/Archiv/languages.pdf

LINKS

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, 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

Eric Weisstein's World of Mathematics, Semigroup.

Index entries for sequences related to semigroups

CROSSREFS

a(n)=A001423(n)*2-A029851(n). Cf. A001426, A023814, A058108.

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

Sequence in context: A009601 A009676 A192995 * A120765 A259355 A051812

Adjacent sequences:  A027848 A027849 A027850 * A027852 A027853 A027854

KEYWORD

nonn,hard,nice

AUTHOR

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

EXTENSIONS

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

STATUS

approved

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Last modified May 6 18:32 EDT 2016. Contains 272508 sequences.