A118100 Number of commutative semigroups of order <= n.

1, 2, 5, 17, 75, 400, 2543, 19834, 241639

Offset

0,2

Comments

A001426(n) is the number of commutative semigroups of order n. A001426(n) + A079193(n) + A079196(n) + A079199(n) = A001329(n). 2, 5, 17, 2543 and 241639 are primes.

Links

Table of n, a(n) for n=0..8.

Index entries for sequences related to semigroups.

Formula

a(n) = SUM[i=1..n] A001426(i).

Example

a(8) = 1 + 1 + 3 + 12 + 58 + 325 + 2143 + 17291 + 221805 = 241639.

Crossrefs

Cf. A001423, A001426, A023815, A027851, A058105, A058116.

Sequence in context: A260948 A259870 A348878 * A129591 A328439 A328504

Adjacent sequences: A118097 A118098 A118099 * A118101 A118102 A118103

Keyword

nonn

Author

Jonathan Vos Post, May 11 2006

Status

approved