What is the Greatest Common Factor of 645 and 665?

Greatest common factor (GCF) of 645 and 665 is 5.

GCF(645,665) = 5

We will now calculate the prime factors of 645 and 665, than find the greatest common factor (greatest common divisor (gcd)) of the numbers by matching the biggest common factor of 645 and 665.

How to find the GCF of 645 and 665?

We will first find the prime factorization of 645 and 665. After we will calculate the factors of 645 and 665 and find the biggest common factor number .

Step-1: Prime Factorization of 645

Prime factors of 645 are 3, 5, 43. Prime factorization of 645 in exponential form is:

645 = 3¹ × 5¹ × 43¹

Step-2: Prime Factorization of 665

Prime factors of 665 are 5, 7, 19. Prime factorization of 665 in exponential form is:

665 = 5¹ × 7¹ × 19¹

Step-3: Factors of 645

List of positive integer factors of 645 that divides 645 without a remainder.

1, 3, 5, 15, 43, 129, 215

Step-4: Factors of 665

List of positive integer factors of 665 that divides 645 without a remainder.

1, 5, 7, 19, 35, 95, 133

Final Step: Biggest Common Factor Number

We found the factors and prime factorization of 645 and 665. The biggest common factor number is the GCF number.
So the greatest common factor 645 and 665 is 5.

Also check out the Least Common Multiple of 645 and 665