# Greatest Common Factor of 15 and 21

Greatest common factor (GCF) of 15 and 21 is 3.

GCF(15,21) = 3

We will now calculate the prime factors of 15 and 21, than find the greatest common factor (greatest common divisor (gcd)) of the numbers by matching the biggest common factor of 15 and 21.

GCF Calculator and

## Prime Factorization of 15

Prime factors of 15 are 3, 5. Prime factorization of 15 in exponential form is:

15 = 31 × 51

## Prime Factorization of 21

Prime factors of 21 are 3, 7. Prime factorization of 21 in exponential form is:

21 = 31 × 71

### Factors of 15

List of positive integer factors of 15 that divides 15 without a remainder.

1, 3, 5

### Factors of 21

List of positive integer factors of 21 that divides 15 without a remainder.

1, 3, 7

### Greatest Common Factor

We found the factors and prime factorization of 15 and 21. The biggest common factor number is the GCF number.
So the greatest common factor 15 and 21 is 3.

Also check out the Least Common Multiple of 15 and 21