A293511 Numbers that can be written as a product of distinct squarefree numbers in exactly one way.

1, 2, 3, 5, 7, 11, 12, 13, 17, 18, 19, 20, 23, 28, 29, 31, 36, 37, 41, 43, 44, 45, 47, 50, 52, 53, 59, 61, 63, 67, 68, 71, 73, 75, 76, 79, 83, 89, 92, 97, 98, 99, 100, 101, 103, 107, 109, 113, 116, 117, 120, 124, 127, 131, 137, 139, 147, 148, 149, 151, 153

Offset

1,2

Comments

First differs from A212166 at a(128) = 363, A212166(128) = 360.

Links

Table of n, a(n) for n=1..61.

Example

360 is not in the sequence because it has two possible expressions: 2*3*6*10 or 2*6*30.

Mathematica

nn=300;
sqfacs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[sqfacs[n/d], Min@@#>d&]], {d, Select[Rest[Divisors[n]], SquareFreeQ]}]];
Select[Range[nn], Length[sqfacs[#]]===1&]

Crossrefs

Cf. A001055, A005117, A045778, A050320, A050326, A292432, A292444, A293243.

Sequence in context: A182358 A336418 A212166 * A336615 A325337 A342119

Adjacent sequences: A293508 A293509 A293510 * A293512 A293513 A293514

Keyword

nonn

Author

Gus Wiseman, Oct 11 2017

Status

approved