OFFSET
1,3
COMMENTS
LINKS
EXAMPLE
The a(26) = 4 factorizations of 45 into stable numbers:
(3*3*5)
(3*15)
(5*9)
(45)
The a(201) = 11 multiset partitions of the prime indices of 495 into stable multisets:
{{2},{2},{3},{5}}
{{2},{2},{3,5}}
{{2},{3},{2,5}}
{{2},{5},{2,3}}
{{2},{2,3,5}}
{{3},{2,2},{5}}
{{3},{2,2,5}}
{{2,2},{3,5}}
{{5},{2,2,3}}
{{2,3},{2,5}}
{{2,2,3,5}}
MATHEMATICA
nn=100;
facsusing[s_, n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[facsusing[Select[s, Divisible[n/d, #]&], n/d], Min@@#>=d&]], {d, Select[s, Divisible[n, #]&]}]];
stableQ[u_, Q_]:=!Apply[Or, Outer[#1=!=#2&&Q[#1, #2]&, u, u, 1], {0, 1}];
y=Select[Range[nn], stableQ[PrimePi/@First/@FactorInteger[#], Divisible]&];
Table[Length[facsusing[Rest[y], n]], {n, y}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Sep 15 2019
STATUS
approved