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

Author

Geoffrey Critzer, May 17 2023

Keywords

• nonn
• tabl
• more

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.

Crossrefs

Cf. A354279 (row sums), A003425 (main diagonal), A060867 (column k=1), A354741.