In that case, one of the numbers is a multiple of the other.
They are called relative prime numbers.
Here are pairs of numbers with 6 as their greatest common factor: 6, 18 12, 30 120, 126 306, 318 6 and 12
The factor pairs of 8 are (8,1)(4,2) The GCF requires at least two numbers.
14 and 21, and 21 and 28 are the number pairs between 15 and 30 that have 7 as their greatest common factor.
An infinite number of number pairs have a greatest common factor of 850. One example is 1700 and 2550.
5 and 10 10 and 15
10 and 15
6 and 12 6 and 18
8 and 16 8 and 24
7 and 14 21 and 28
200,205 15,20 65,75 85,100
16 and 32 among many others.