A363036 Triangular array read by rows. T(n,k) is the number of regular elements in the semigroup of all binary relations on [n] that have rank k, n>=0, 0<=k<=n.
1, 1, 1, 1, 9, 6, 1, 49, 306, 114, 1, 225, 8550, 26376, 5256, 1, 961, 194850, 3311250, 4669200, 507720
Offset: 0
Examples
1; 1, 1; 1, 9, 6; 1, 49, 306, 114; 1, 225, 8550, 26376, 5256; 1, 961, 194850, 3311250, 4669200, 507720; ...
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.