OFFSET
1,3
COMMENTS
A relatively prime p-tree of weight n is either a single node, or a finite sequence of two or more relatively prime p-trees whose weights are weakly decreasing, relatively prime, and sum to n.
EXAMPLE
The a(4) = 4 relatively prime p-trees are (((oo)o)o), ((ooo)o), ((oo)oo), (oooo). Missing from this list is the p-tree ((oo)(oo)).
MATHEMATICA
a[n_]:=a[n]=If[n===1, 1, Sum[Times@@a/@y, {y, Rest[Select[IntegerPartitions[n], Or[Length[#]===1, GCD@@#===1]&]]}]];
Array[a, 20]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Apr 15 2018
STATUS
approved