Semigroup/Talk

Question: How many semigroups are there of a given finite order? Is there a formula?

I doubt that there's a known formula.

• http://www.research.att.com/cgi-bin/access.cgi/as/njas/sequences/eisA.cgi?Anum=A023814 for the total number of semigroups on a set with n elements
• http://www.research.att.com/cgi-bin/access.cgi/as/njas/sequences/eisA.cgi?Anum=A027851 for the number of non-isomorphic semigroups with n elements --AxelBoldt