There cannot be a greatest common factor if there are not at least two numbers to compare. The greatest common factor is the largest factor that all the numbers have in common - the largest factor that they all share.
The greatest common factor of 39 and 18 is definitely 3.
The greatest common factor of 30 and 39 is 3.
The greatest common factor is 5 * * * * * Actually, it is 39
The greatest common factor of 37 and 39 is 1.
The greatest common factor of 90 and 39 is 3
Greatest common factor of 39 and 104 is 13.
The greatest common factor of 22 and 39 is 1
The Greatest Common Factor of 39, 48, 51: 3
The greatest common factor of 33, 27 & 39 is 3.
The greatest common factor of 3 and 39 is 3.
The greatest common factor of the numbers 39, 13 and 26 is 13.
The Greatest Common Factor (GCF) is: 1