Prime Numbers
What Is a Prime Number?
A prime number is a number that can be divided by only itself and 1.
For example,

2 is a prime number. It can only be divided exactly by 1 and 2 itself.

3 is a prime number. It can only be divided exactly by 1 and 3 itself.

4 is not a prime number. It can be divided exactly by 1, 2 and 4.
Dictionary Definition
The Oxford English Dictionary defines a prime number as "a number that cannot be divided by any whole number (without a remainder) other than itself and one."
The Prime Numbers
The prime numbers are:
In a number square, the prime numbers are shaded below:
These are just the prime numbers under 100. There are infinitely many prime numbers, they go on forever.