OFFSET
1,3
COMMENTS
An unlabeled rooted tree is fully anti-transitive if no proper terminal subtree of any branch of the root is a branch of the root.
EXAMPLE
The a(1) = 1 through a(6) = 11 rooted trees:
o (o) (oo) (ooo) (oooo) (ooooo)
((o)) ((oo)) ((ooo)) ((oooo))
(((o))) (((oo))) (((ooo)))
((o)(o)) ((o)(oo))
((o(o))) ((o(oo)))
((((o)))) ((oo(o)))
((((oo))))
(((o)(o)))
(((o(o))))
((o((o))))
(((((o)))))
MATHEMATICA
rtall[n_]:=Union[Sort/@Join@@(Tuples[rtall/@#]&/@IntegerPartitions[n-1])];
Table[Length[Select[rtall[n], Intersection[Union@@Rest[FixedPointList[Union@@#&, #]], #]=={}&]], {n, 10}]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Mar 17 2019
EXTENSIONS
a(17)-a(20) from Jinyuan Wang, Jun 20 2020
STATUS
approved