OFFSET
1,4
EXAMPLE
The a(1) = 1 through a(6) = 10 rooted trees:
o ((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
submultQ[cap_, fat_]:=And@@Function[i, Count[fat, i]>=Count[cap, i]]/@Union[List@@cap];
rtall[n_]:=Union[Sort/@Join@@(Tuples[rtall/@#]&/@IntegerPartitions[n-1])];
Table[Length[Select[rtall[n], And@@Table[!submultQ[b, #], {b, #}]&]], {n, 10}]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Mar 18 2019
STATUS
approved