

A027851


Number of nonisomorphic semigroups of order n.


18




OFFSET

0,3


REFERENCES

A. de Vries, Formal Languages: An Introduction, http://haegar.fhswf.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 nearrings
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)*2A029851(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



