If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Lesson 2: Prime and composite numbers

# Prime and composite numbers review

Review prime and composite numbers, and try some practice problems.

## What are prime numbers?

Prime numbers are numbers with exactly $2$ factors.
A prime number's only factors are $1$ and the number $\text{itself}$.
$7$ is an example of a prime number. Its only factors are $1$ and $7$. It is not evenly divisible by any other whole numbers.

## Practice set 1: Identifying prime numbers

Problem 1A
Which of these numbers is prime?

Want to try more problems like this? Check out this exercise.

## What are composite numbers?

Composite numbers have more than $2$ factors. A composite number has factors in addition to $1$ and the number $\text{itself}$.
$16$ is an example of a composite number. The factors of $16$ are $1,2,4,8$ and $16.$ All of these numbers divide into $16$ evenly.

## Practice set 2: Identifying composite numbers

Problem 2A
Which of these numbers is composite?

Want to try more problems like this? Check out this exercise.

## Want to join the conversation?

• How did scientists discover about prime numbers
Edit: that was a weird question….
• I actually have no idea. But I imagine that a mathematician found out that some numbers can only be divided by one and itself. But I am not sure.
• is 2 the only even prime number
• Yes because all other even numbers are divisible by 2
• One question about this: is 1 a prime or a composite number? Neither of those numbers.
• Its a neither because it is cannot be divisible by 2 natural number or it has only on factor
• Is 1 a prime number or a compsite number?
• It is neither prime nor composite because it's only factor is 1.
• is 349,860,748,398 a composite or prime?
• Composite. It is divisible by other numbers than 2, such as 3.
• Why is 2 the lone even prime number?
• A number is prime only if it can be divided by 1 and itself. Because the only factors of 2 are 1 and 2, 2 matches the definition of a prime number and is, therefore, prime.
• whats the point of learning about prime and composites if no one really uses them outside of school?