A391160 Number of nonisomorphic semigroups with n elements and empty center.

1, 0, 2, 6, 55, 552, 7954, 143958

Offset

0,3

Links

Table of n, a(n) for n=0..7.

Wikipedia, Center (algebra).

Index entries for sequences related to semigroups.

Example

The Cayley tables of the a(2) = 2 semigroups are:
     1 1   1 2
     2 2   1 2
The Cayley tables of the a(3) = 6 semigroups are:
  1 1 3   1 1 1   1 1 3   1 1 1   1 2 3   1 1 1
  1 1 3   1 1 1   1 2 3   1 2 1   1 2 3   2 2 2
  1 1 3   3 3 3   1 1 3   3 3 3   1 2 3   3 3 3

Crossrefs

Column k=0 of A391159.

Cf. A391156, A391158 (labeled version).

Sequence in context: A153450 A179389 A084123 * A193473 A336899 A181509

Adjacent sequences: A391157 A391158 A391159 * A391161 A391162 A391163

Keyword

nonn,more

Author

Andrew Howroyd, Dec 10 2025

Status

approved