A350910 Triangle read by rows: T(n,k) is the number of k-regular digraphs on n unlabeled nodes, k = 0..n-1.

1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 2, 5, 2, 1, 1, 4, 23, 23, 4, 1, 1, 4, 92, 415, 92, 4, 1, 1, 7, 624, 19041, 19041, 624, 7, 1, 1, 8, 5021, 1104045, 6510087, 1104045, 5021, 8, 1, 1, 12, 47034, 79818336, 2983458766, 2983458766, 79818336, 47034, 12, 1

Offset: 1

Author

Andrew Howroyd, Jan 29 2022

Keywords

• nonn
• tabl

Examples

			Triangle begins:
  1;
  1, 1;
  1, 1,   1;
  1, 2,   2,     1;
  1, 2,   5,     2,     1;
  1, 4,  23,    23,     4,   1;
  1, 4,  92,   415,    92,   4, 1;
  1, 7, 624, 19041, 19041, 624, 7, 1;
  ...
		

Crossrefs

Columns k=0..6 are A000012, A002865, A219889, A219890, A219891, A219892, A219893.

Row sums are A350911.

Cf. A051031 (graphs), A329228 (semi-regular), A350912.