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

1,3

Links

Table of n, a(n) for n=1..10.

Example

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.

Sequence in context: A192637 A111916 A328440 * A118187 A307773 A332776

Adjacent sequences: A308631 A308632 A308633 * A308635 A308636 A308637

Keyword

nonn,more

Author

Adam P. Goucher, Jun 12 2019

Status

approved