OFFSET
1,2
COMMENTS
LINKS
R. E. Canfield, P. Erdős and C. Pomerance, On a Problem of Oppenheim concerning "Factorisatio Numerorum", J. Number Theory 17 (1983), 1-28.
EXAMPLE
Factorizations of n for n = 4, 8, 12, 16, 24, 36, 48, 60:
4 8 12 16 24 36 48 60
2*2 2*4 2*6 2*8 3*8 4*9 6*8 2*30
2*2*2 3*4 4*4 4*6 6*6 2*24 3*20
2*2*3 2*2*4 2*12 2*18 3*16 4*15
2*2*2*2 2*2*6 3*12 4*12 5*12
2*3*4 2*2*9 2*3*8 6*10
2*2*2*3 2*3*6 2*4*6 2*5*6
3*3*4 3*4*4 3*4*5
2*2*3*3 2*2*12 2*2*15
2*2*2*6 2*3*10
2*2*3*4 2*2*3*5
2*2*2*2*3
MATHEMATICA
nn=1000;
facs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[facs[n/d], Min@@#>=d&]], {d, Rest[Divisors[n]]}]];
nds=Length/@Array[facs, nn];
Table[Position[nds, i][[1, 1]], {i, First/@Gather[nds]}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jan 06 2020
STATUS
approved