A118100 - OEIS

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A118100

Number of commutative semigroups of order <= n.

0

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

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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