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A079175
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Number of isomorphism classes of associative closed binary operations (semigroups) on a set of order n, listed by class size.
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5
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1, 1, 2, 3, 2, 0, 7, 15, 2, 0, 0, 7, 5, 0, 62, 112, 2, 0, 0, 0, 6, 0, 0, 8, 0, 2, 51, 0, 47, 2, 576, 1221, 2, 0, 0, 0, 0, 6, 0, 0, 0, 0, 8, 0, 0, 4, 0, 48, 0, 0, 0, 0, 92, 0, 0, 42, 506, 0, 813, 32, 7397, 19684, 2, 0, 0, 0, 0, 0, 6, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8
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OFFSET
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0,3
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COMMENTS
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Elements per row: 1,1,2,4,8,16,30,... (given by A027423, number of positive divisors of n!)
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LINKS
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FORMULA
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EXAMPLE
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Triangle T(n,k) begins:
1;
1;
2, 3;
2, 0, 7, 15;
2, 0, 0, 7, 5, 0, 62, 112;
2, 0, 0, 0, 6, 0, 0, 8, 0, 2, 51, 0, 47, 2, 576, 1221;
...
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CROSSREFS
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KEYWORD
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nonn,tabf
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AUTHOR
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Christian van den Bosch (cjb(AT)cjb.ie), Jan 03 2003
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EXTENSIONS
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a(0)=1 prepended and terms a(16) and beyond from Andrew Howroyd, Jan 26 2022
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STATUS
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approved
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