Prime Numbers
(KS2, Year 4)

The Lesson

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.

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.

Prime Numbers Are Natural Numbers Greater Than 1

Prime numbers are natural numbers (the counting numbers: 1, 2, 3...) greater than 1. 1 is not a prime number, even though it can only be divided by 1 and itself. Some times in history is has been considered a prime number, but now it is not.

Interactive Game on Prime Numbers

Here is an interactive game to help you learn about prime numbers.

• You are the fish.
• Pop the bubbles with prime numbers to collect red hearts. You need five to win.
• If a bubble with an prime number reaches the top, you will lose a red heart.
• Avoid the bubbles with composite numbers (i.e., non-prime numbers). If you pop one, you will lose one of your three lives.
• Good luck!
• The fish moves to wherever you taptowards your mouse clicks. (Hint: The farther the distance, the faster it moves.)

Factors

Numbers that divide exactly into another number are called factors. For example, the factors of 4 are 1, 2 and 4 because they all divide exactly into 4. Prime numbers only have two factors, 1 and the prime number itself. The only factors of 2 are 1 and 2. The only factors of 3 are 1 and 3. The only factors of 5 are 1 and 5.