cp's OEIS Frontend

A139623 Table read by rows: T(n,k) is the number of directed multigraphs with loops and no vertex of degree 0, with n arcs and k vertices, which are transitive (the existence of a path between two points implies the existence of an arc between those two points).

%I A139623 #14 Jul 29 2020 13:16:44
%S A139623 1,1,1,4,3,1,1,7,12,9,3,1,1,13
%N A139623 Table read by rows: T(n,k) is the number of directed multigraphs with loops and no vertex of degree 0, with n arcs and k vertices, which are transitive (the existence of a path between two points implies the existence of an arc between those two points).
%C A139623 Length of the n^th row: 2n.
%C A139623 T(n,1) = T(n,2n) = 1 and T(n,2n-1) = 3 if n>1.
%C A139623 Row sums: A139628.
%e A139623 Triangle begins
%e A139623 1, 1;
%e A139623 1, 4, 3, 1;
%e A139623 1, 7, 12, 9, 3, 1;
%Y A139623 Cf. A136564, A139624, A139625.
%K A139623 nonn,tabf,more
%O A139623 1,4
%A A139623 _Benoit Jubin_, May 01 2008