OFFSET
1,2
EXAMPLE
The strict factorizations of a(n) for n = 1..9.
{} 6 12 24 48 60 64 96 120
2*3 2*6 3*8 6*8 2*30 2*32 2*48 2*60
3*4 4*6 2*24 3*20 4*16 3*32 3*40
2*12 3*16 4*15 2*4*8 4*24 4*30
2*3*4 4*12 5*12 6*16 5*24
2*3*8 6*10 8*12 6*20
2*4*6 2*5*6 2*6*8 8*15
3*4*5 3*4*8 10*12
2*3*10 2*3*16 3*5*8
2*4*12 4*5*6
2*3*20
2*4*15
2*5*12
2*6*10
3*4*10
2*3*4*5
MATHEMATICA
nn=1000;
strfacs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[strfacs[n/d], Min@@#>d&]], {d, Rest[Divisors[n]]}]];
nds=Length/@Array[strfacs, nn];
Table[Position[nds, i][[1, 1]], {i, First/@Gather[nds]}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jan 06 2020
STATUS
approved