What is the Greatest Common Factor of 18 and 21?
Greatest common factor (GCF) of 18 and 21 is 3.
GCF(18,21) = 3
We will now calculate the prime factors of 18 and 21, than find the greatest common factor (greatest common divisor (gcd)) of the numbers by matching the biggest common factor of 18 and 21.
How to find the GCF of 18 and 21?
We will first find the prime factorization of 18 and 21. After we will calculate the factors of 18 and 21 and find the biggest common factor number .
Step-1: Prime Factorization of 18
Prime factors of 18 are 2, 3. Prime factorization of 18 in exponential form is:
18 = 21 × 32
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 18
List of positive integer factors of 18 that divides 18 without a remainder.
1, 2, 3, 6, 9
Step-4: Factors of 21
List of positive integer factors of 21 that divides 18 without a remainder.
1, 3, 7
Final Step: Biggest Common Factor Number
We found the factors and prime factorization of 18 and 21. The biggest common factor number is the GCF number.
So the greatest common factor 18 and 21 is 3.
Also check out the Least Common Multiple of 18 and 21