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A308634
Number of triangle-free acyclic digraphs (or DAGs) up to isomorphism with n vertices, maximum indegree 2 and unique maximal element.
0
1, 1, 2, 5, 18, 81, 475, 3394, 29140, 293198
OFFSET
1,3
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
KEYWORD
nonn,more
AUTHOR
Adam P. Goucher, Jun 12 2019
STATUS
approved