A308634 Number of triangle-free acyclic digraphs (or DAGs) up to isomorphism with n vertices, maximum indegree 2 and unique maximal element.

1, 1, 2, 5, 18, 81, 475, 3394, 29140, 293198

Offset: 1

Author

Adam P. Goucher, Jun 12 2019

Keywords

• nonn
• more

Examples

			a(1) = 1, a(2) = 1 and a(3) = 2 coincide with the first three terms of A001190, as all connected triangle-free DAGs with at most three vertices are necessarily trees.
For n = 4, the a(4) = 5 solutions are the following three trees:
(((())))
((), (()))
(((), ()))
together with two 4-cycles.
		

Crossrefs

Lower-bounded by A001190.