1
The common factor is 1.
Since 17 is a prime number, the greatest common factor of 17, 18, and 20 is 1.
The only common factor is 1.
There is no common factor for 17, 18, and 70 other than one.
The least common factor of any set of numbers is 1.
The only common factor is 1.
18
The GCF is 1.
The GCF is 1.
The GCF is 1.
The GCF is 1.