A023814 Number of associative binary operations on an n-set; number of labeled semigroups.

1, 1, 8, 113, 3492, 183732, 17061118, 7743056064, 148195347518186, 38447365355811944462

Offset: 0

Author

Lyle Ramshaw (ramshaw(AT)pa.dec.com)

Keywords

• nonn
• more

Links

• Alex Bailey, Martin Finn-Sell, and Robert Snocken, Subsemigroup, ideal and congruence growth of free semigroups, arXiv preprint arXiv:1409.2444 [math.GR], 2014.
• 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 [broken link]
• 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

Cf. A001423, A001426, A023813, A023815, A027851.

a(n) + A079172(n) = A002489(n).

Extensions

a(8), a(9) from Distler and Kelsey (2013). - N. J. A. Sloane, Feb 19 2013