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A173311
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a(n) is the number of regular D classes in the semigroup of all binary relations on [n].
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1
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1, 2, 4, 9, 25, 88, 406, 2451, 19450, 202681, 2769965, 49519392, 1154411138, 34978238590, 1373171398361, 69648249299517, 4552778914494604
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OFFSET
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0,2
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COMMENTS
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Previous name was: Partial sums of A000112.
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LINKS
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Table of n, a(n) for n=0..16.
K. K.-H. Butler and G. Markowsky, The Number of Maximal Subgroups of the Semigroup of Binary Relations, Kyungpook Math. J. Vol 12, June 1972.
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FORMULA
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a(n) = Sum_{i=0..n} A000112(i).
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MATHEMATICA
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Cases[Import["https://oeis.org/A000112/b000112.txt", "Table"], {_, _}][[All, 2]] // Accumulate (* Jean-François Alcover, Jan 01 2020 *)
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CROSSREFS
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Cf. A000112, A000798 (labeled topologies), A001035 (labeled posets), A001930 (unlabeled topologies), A006057, A079263, A079265, A007903.
Sequence in context: A192801 A270954 A173496 * A127055 A124835 A125799
Adjacent sequences: A173308 A173309 A173310 * A173312 A173313 A173314
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KEYWORD
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nonn,hard,more
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AUTHOR
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Jonathan Vos Post, Feb 16 2010
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EXTENSIONS
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New name from Geoffrey Critzer, May 22 2022
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STATUS
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approved
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