A305150 Number of factorizations of n into distinct, pairwise indivisible factors greater than 1.

1, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 2, 1, 2, 2, 1, 1, 2, 1, 2, 2, 2, 1, 3, 1, 2, 1, 2, 1, 5, 1, 1, 2, 2, 2, 2, 1, 2, 2, 3, 1, 5, 1, 2, 2, 2, 1, 3, 1, 2, 2, 2, 1, 3, 2, 3, 2, 2, 1, 6, 1, 2, 2, 1, 2, 5, 1, 2, 2, 5, 1, 3, 1, 2, 2, 2, 2, 5, 1, 3, 1, 2, 1, 6, 2, 2, 2, 3, 1, 6, 2, 2, 2, 2, 2, 4, 1, 2, 2, 2, 1, 5, 1, 3, 5

Offset: 1

Author

Gus Wiseman, May 26 2018

Keywords

• nonn

Examples

			The a(60) = 6 factorizations are (3 * 4 * 5), (3 * 20), (4 * 15), (5 * 12), (6 * 10), (60). Missing from this list are (2 * 3 * 10), (2 * 5 * 6), (2 * 30).
		

Links

• Antti Karttunen, Table of n, a(n) for n = 1..16384
• Antti Karttunen, Data supplement: n, a(n) computed for n = 1..100000

Crossrefs

Cf. A001055, A001970, A007716, A045778, A162247, A259936, A275024, A285572, A281113, A281116, A303386, A303431, A305001, A305148, A305149, A305253.

Programs

Mathematica

facs[n_] := If[n <= 1, {{}}, Join@@Table[Map[Prepend[#, d] &, Select[facs[n/d], Min@@ # >= d &]], {d, Rest[Divisors[n]]}]]; Table[Length[Select[facs[n], UnsameQ@@ # && Select[Tuples[Union[#], 2], UnsameQ@@ # && Divisible@@ # &] == {} &]], {n, 100}]

PARI

A305150(n, m=n, facs=List([])) = if(1==n, 1, my(s=0, newfacs); fordiv(n, d, if((d>1)&&(d<=m)&&factorback(apply(x -> (x%d),Vec(facs))), newfacs = List(facs); listput(newfacs,d); s += A305150(n/d, d-1, newfacs))); (s)); \\ Antti Karttunen, Dec 06 2018

Formula

a(n) <= A045778(n) <= A001055(n). - Antti Karttunen, Dec 06 2018

Extensions

More terms from Antti Karttunen, Dec 06 2018