The greatest common factor (GCF) is the greatest number that is a factor of two or more numbers. The first step for finding a GCF is to break down each number into its prime factors. We will write down all of the prime factors that are common between the given numbers.
Given number
Prime Factorization
Common Prime Factors
21
7* 3
7
49
7* 7
7
For the given values, the only common prime factor is 7. So, 7 is the greatest common factor of 21 and 49.
