GCF for 21 and 81

"Greatest Common Factor" Calculator

Greatest Common Factor of

and

What is the Greatest common Divisor of 21 and 81?

Answer: GCF of 21 and 81 is 3

(Three)

Finding GCF for 21 and 81 using all factors (divisors) listing

The first method to find GCF for numbers 21 and 81 is to list all factors for both numbers and pick the highest common one:

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

All factors of 81: 1, 3, 9, 27, 81

So the Greatest Common Factor for 21 and 81 is 3

Finding GCF for 21 and 81 by Prime Factorization

The second method to find GCF for numbers 21 and 81 is to list all Prime Factors for both numbers and multiply the common ones:

All Prime Factors of 21: 3, 7

All Prime Factors of 81: 3, 3, 3, 3

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 21 and 81

See Also

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 21 and 81? (The answer is: 3). Select the first number (e.g. '21') and the second number (e.g. '81'). 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
6813
7811
8811
9819
10811
11811
12813
13811
14811
15813
16811
17811
18819
19811
20811
21813
22811
23811
24813
25811
26811
278127
28811
29811
30813
31811
32811
33813
34811
35811

FAQ

What is the Greatest common Divisor of 21 and 81?

GCF of 21 and 81 is 3

See Also