A173311 a(n) is the number of regular D classes in the semigroup of all binary relations on [n].
1, 2, 4, 9, 25, 88, 406, 2451, 19450, 202681, 2769965, 49519392, 1154411138, 34978238590, 1373171398361, 69648249299517, 4552778914494604
Offset: 0
Links
- 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.
Crossrefs
Programs
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Mathematica
Cases[Import["https://oeis.org/A000112/b000112.txt", "Table"], {, }][[All, 2]] // Accumulate (* Jean-François Alcover, Jan 01 2020 *)
Formula
a(n) = Sum_{i=0..n} A000112(i).
Extensions
New name from Geoffrey Critzer, May 22 2022
Comments