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A118100
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Number of commutative semigroups of order <= n.
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0
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OFFSET
| 0,2
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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.
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LINKS
| Index entries for sequences related to semigroups.
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FORMULA
| a(n) = SUM[i=1..n] A001426(i).
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EXAMPLE
| a(8) = 1 + 1 + 3 + 12 + 58 + 325 + 2143 + 17291 + 221805 = 241639.
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CROSSREFS
| Cf. A001423, A001426, A023815, A027851, A058105, A058116.
Sequence in context: A112831 A081046 A000774 * A129591 A099825 A014288
Adjacent sequences: A118097 A118098 A118099 * A118101 A118102 A118103
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KEYWORD
| nonn
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AUTHOR
| Jonathan Vos Post (jvospost3(AT)gmail.com), May 11 2006
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