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

0,5

Links

Table of n, a(n) for n=0..20.

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.

Example

 1;
 1,   1;
 1,   9,      6;
 1,  49,    306,     114;
 1, 225,   8550,   26376,    5256;
 1, 961, 194850, 3311250, 4669200, 507720;
 ...

Crossrefs

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

Sequence in context: A220669 A064230 A286331 * A354741 A355333 A089479

Adjacent sequences: A363033 A363034 A363035 * A363037 A363038 A363039

Keyword

nonn,tabl,more

Author

Geoffrey Critzer, May 17 2023

Status

approved