OFFSET
1,3
COMMENTS
Row sums of A298426.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..200
FORMULA
a(n) = 2 <=> n in {A008864}. - Alois P. Heinz, Jan 20 2018
EXAMPLE
The a(9) = 6 trees: ((((((((o)))))))), (o(o(o(oo)))), (o((oo)(oo))), ((oo)(o(oo))), (ooo(oooo)), (oooooooo).
MATHEMATICA
srut[n_]:=srut[n]=If[n===1, {{}}, Select[Join@@Function[c, Union[Sort/@Tuples[srut/@c]]]/@Select[IntegerPartitions[n-1], Function[ptn, And@@(Divisible[#-1, Length[ptn]]&/@ptn)]], SameQ@@Length/@Cases[#, {__}, {0, Infinity}]&]];
Table[srut[n]//Length, {n, 20}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jan 19 2018
EXTENSIONS
a(44)-a(52) from Alois P. Heinz, Jan 20 2018
STATUS
approved