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## Understanding Prime Numbers

#### Introduction

A Prime Number is a number that cannot be evenly divided by any other whole number other than 1 and itself. So 1, 2, 3 and 5 are all prime numbers, but 4 is not, since 4 can not only be divided by 1 and 4, but 2 as well.

#### Terms

Prime Number - A prime number is a number that cannot be evenly divided by any number other than 1 and itself.

## Lesson

A prime number is a number that is not evenly divisible by any number other than 1 or itself. So if we are asked to list all the prime numbers between 1 and 10, we could determine the answer by considering each number between 1 and 10, and determining whether it has any factors other than 1 and itself.

NumberFactors
11
21, 2
31, 3
41, 2, 4
51, 5
61, 2, 3, 6
71, 7
81, 2, 4, 8
91, 3, 3, 9
101, 2, 5, 10

Essentially, any number that has an entry in the 'Other Factors' column is not a prime factor. So the prime numbers between 1 and 10 are 1, 2, 3, 5 and 7.

(Fun Fact: Did you know that '2' is the only even prime number?)

## Examples

#### Picking Prime Numbers

Which of the whole numbers are prime numbers?
The factors of are . Therefore is a prime number.
The factors of are . Therefore is not a prime number.
The factors of are . Therefore is not a prime number.
The factors of are . Therefore is a prime number.

#### Listing Prime Numbers

List All Prime Numbers Between
List prime numbers between and
are the prime numbers between and

#### Picking Prime Numbers

Which of the whole numbers are prime numbers?
The factors of are . Therefore is not a prime number.
The factors of are . Therefore is a prime number.
The factors of are . Therefore is not a prime number.
The factors of are . Therefore is a prime number.

#### Listing Prime Numbers

List All Prime Numbers Between
List prime numbers between and
are the prime numbers between and

#### Picking Prime Numbers

Which of the whole numbers are prime numbers?
The factors of are . Therefore is not a prime number.
The factors of are . Therefore is a prime number.
The factors of are . Therefore is a prime number.
The factors of are . Therefore is not a prime number.