GCF for 15 and 21

"Greatest Common Factor" Calculator

Greatest Common Factor of

and

What is the Greatest common Divisor of 15 and 21?

Answer: GCF of 15 and 21 is 3

(Three)

Finding GCF for 15 and 21 using all factors (divisors) listing

The first method to find GCF for numbers 15 and 21 is to list all factors for both numbers and pick the highest common one:

All factors of 15: 1, 3, 5, 15

All factors of 21: 1, 3, 7, 21

So the Greatest Common Factor for 15 and 21 is 3

Finding GCF for 15 and 21 by Prime Factorization

The second method to find GCF for numbers 15 and 21 is to list all Prime Factors for both numbers and multiply the common ones:

All Prime Factors of 15: 3, 5

All Prime Factors of 21: 3, 7

As we can see there is only one Prime Factor common to both numbers. It is 3

So 3 is the Greatest Common Factor of 15 and 21

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About "Greatest Common Factor" Calculator

This calculator will help you find the greatest common factor (GCF) of two numbers. For example, it can help you find out what is the Greatest common Divisor of 15 and 21? (The answer is: 3). Select the first number (e.g. '15') and the second number (e.g. '21'). After that hit the 'Calculate' button.
Greatest Common Factor (GCF) also known as the Greatest Common Divisor (GCD) or Highest Common Factor (HCF) - it is the largest positive integer that divides each of the integers with zero remainder

"Greatest Common Factor" Calculator

Greatest Common Factor of

and

GCF Table

Number 1Number 2GCF
1211
2211
3213
4211
5211
6213
7217
8211
9213
10211
11211
12213
13211
14217
15213
16211
17211
18213
19211
20211
212121
22211
23211
24213
25211
26211
27213
28217
29211
30213

FAQ

What is the Greatest common Divisor of 15 and 21?

GCF of 15 and 21 is 3

See Also