There cannot be a greatest common factor (GCF) of just one number. To be common there need to be at least two numbers. If you find all the factors of two or more numbers, and you find some factors are the same ("common"), then the largest of those common factors is the Greatest Common Factor.
The greatest common factor of 61 and 46 is 1.
The greatest common factor of 54 , 61 = 1
The greatest common factor of 61 , 37 = 1
The Greatest Common Factor (GCF) of 61 and 91 is: 1
61
The GCF is 1.
The Greatest Common Factor (GCF) is: 1
The GCF is 61.
The greatest common factor of 31 and 46 is 1.
61 and 80 don't have a common factor (except 1 which doesn't count).
It is: 1
It is: 1