# What is the Greatest Common Factor of 7 and 21?

Greatest common factor (GCF) of 7 and 21 is 7.

GCF(7,21) = 7

We will now calculate the prime factors of 7 and 21, than find the greatest common factor (greatest common divisor (gcd)) of the numbers by matching the biggest common factor of 7 and 21.

GCF Calculator and
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## How to find the GCF of 7 and 21?

We will first find the prime factorization of 7 and 21. After we will calculate the factors of 7 and 21 and find the biggest common factor number .

### Step-1: Prime Factorization of 7

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

7 = 71

### Step-2: Prime Factorization of 21

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

21 = 31 × 71

### Step-3: Factors of 7

List of positive integer factors of 7 that divides 7 without a remainder.

1

### Step-4: Factors of 21

List of positive integer factors of 21 that divides 7 without a remainder.

1, 3, 7

#### Final Step: Biggest Common Factor Number

We found the factors and prime factorization of 7 and 21. The biggest common factor number is the GCF number.
So the greatest common factor 7 and 21 is 7.

Also check out the Least Common Multiple of 7 and 21