OFFSET
0,3
COMMENTS
A rooted tree is series-reduced if it has no unary branchings, so every non-leaf node covers at least two other nodes.
EXAMPLE
Non-isomorphic representatives of the a(1) = 1 through a(3) = 10 trees:
{1} {1,2} {1,2,3}
{{1},{1}} {{1},{1,2}}
{{1},{2}} {{1},{2,3}}
{{1},{1},{1}}
{{1},{1},{2}}
{{1},{2},{3}}
{{1},{{1},{1}}}
{{1},{{1},{2}}}
{{1},{{2},{3}}}
{{2},{{1},{1}}}
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Dec 25 2019
STATUS
approved