A350910 - OEIS

%I #8 Jan 29 2022 20:13:46

%S 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,

%T 624,19041,19041,624,7,1,1,8,5021,1104045,6510087,1104045,5021,8,1,1,

%U 12,47034,79818336,2983458766,2983458766,79818336,47034,12,1

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

%e Triangle begins:

%e   1;

%e   1, 1;

%e   1, 1,   1;

%e   1, 2,   2,     1;

%e   1, 2,   5,     2,     1;

%e   1, 4,  23,    23,     4,   1;

%e   1, 4,  92,   415,    92,   4, 1;

%e   1, 7, 624, 19041, 19041, 624, 7, 1;

%e   ...

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

%Y Row sums are A350911.

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

%K nonn,tabl

%O 1,8

%A _Andrew Howroyd_, Jan 29 2022