login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A118100 Number of commutative semigroups of order <= n. 0
1, 2, 5, 17, 75, 400, 2543, 19834, 241639 (list; graph; refs; listen; history; text; internal format)
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: A000774 A260948 A259870 * A129591 A328439 A328504

Adjacent sequences:  A118097 A118098 A118099 * A118101 A118102 A118103

KEYWORD

nonn

AUTHOR

Jonathan Vos Post, May 11 2006

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 22 16:31 EST 2019. Contains 329396 sequences. (Running on oeis4.)