Prime Numbers
(KS2, Year 4)
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:list_of_prime_numbersIn a number square, the prime numbers are shaded below:primes_squareThese 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 a 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 towards your clicks. (Hint: The farther the distance, the faster it moves.)
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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.
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This page was written by Stephen Clarke.