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

0,3

Links

Table of n, a(n) for n=0..9.

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).

Sequence in context: A072402 A346985 A099715 * A217772 A062126 A222520

Adjacent sequences: A023811 A023812 A023813 * A023815 A023816 A023817

Keyword

nonn,more

Author

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

Extensions

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

Status

approved