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 nearrings
Eric Postpischil Posting to sci.math newsgroup, May 21 1990
Jeremy G. Sumner, Michael D. Woodhams, LieMarkov 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
