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 A058167 Triangle read by rows: T(n,k) is the number of labeled commutative semigroups of order n with k idempotents. 2
 1, 4, 2, 24, 30, 9, 260, 492, 312, 76, 4805, 10060, 9900, 4900, 1065, 157956, 284130, 348420, 259500, 112500, 22566, 12277440, 11892846, 14768775, 14093380, 9063600, 3592554, 674611, 3287166928, 896150920, 812261856, 854806120, 707722680, 413149464, 152565280, 27019896 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Table of n, a(n) for n=1..36. Index entries for sequences related to semigroups EXAMPLE Triangle begins: 1; 4, 2; 24, 30, 9; 260, 492, 312, 76; 4805, 10060, 9900, 4900, 1065; ... CROSSREFS Row sums give A023815. Main diagonal is A058164(n+1). Cf. A058116 (isomorphism classes). Sequence in context: A134461 A298593 A228474 * A140331 A095896 A286798 Adjacent sequences: A058164 A058165 A058166 * A058168 A058169 A058170 KEYWORD nonn,tabl,hard AUTHOR Christian G. Bower, Nov 15 2000 EXTENSIONS a(29)-a(36) from Andrew Howroyd, Jan 27 2022 STATUS approved

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Last modified May 30 13:17 EDT 2023. Contains 363050 sequences. (Running on oeis4.)