A118099 Number of inverse semigroups of order <= n.

1, 3, 8, 24, 76, 284, 1195, 5832, 32254, 201417, 1400068, 10724115, 89584802, 809190807, 7844705449

Offset: 1

Author

Jonathan Vos Post, May 11 2006

Keywords

• nonn
• more

Examples

			a(7) = 1195 = 1 + 2 + 5 + 16 + 52 + 208 + 911.
		

References

• M. V. Lawson, Inverse Semigroups: The Theory of Partial Symmetries. Singapore: World Scientific, 1999.
• E. S. Lyapin, Semigroups. Providence, RI: Amer. Math. Soc., 1974.

Links

• Alan Weinstein, Groupoids: Unifying Internal and External Symmetry, Not. Amer. Math. Soc. 43, 744-752, 1996.
• Eric Weisstein et al., Inverse Semigroup.
• Index entries for sequences related to semigroups.

Crossrefs

Partial sums of A001428.

Formula

a(n) = Sum_{i=1..n} A001428(i).

Extensions

More terms from the data at A001428 added by Amiram Eldar, May 03 2023