# Prime and composite numbers

In this lesson, we'll define, compare and contrast prime and composite numbers.

## What are prime numbers?

A prime number is a whole number greater than one which cannot be divided evenly by any other positive whole number except one or itself.

## List of prime numbers

We can't list them all here, but let's consider the first few prime numbers

2      3      5      7      11      13      17      19      23      29      ...

Check out a couple of these numbers to make sure they fit the prime numbers definition.

For example, 3 is a whole number greater than one which cannot be divided evenly by any other positive whole number except 1 and 3 - one and itself.

Similarly, 17's a whole number greater than one, evenly divisible only by the positive whole numbers 1 and 17 - again, one and itself.

## You may find a prime numbers chart useful

Here's a chart of the numbers 1 through 100 with the prime numbers enlarged/highlighted in bold

 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100

Notice how all the prime numbers end in 1, 3, 7 or 9, apart from 2 and 5.

## What are composite numbers?

A composite number is any whole number greater than one which is not a prime number. You can evenly divide a composite number by one, itself and at least one other positive whole number.

For instance

• 4 is a whole number greater than one, evenly divisible by 1, 4 and 2
• 6 is a whole number greater than one, evenly divisible by 1, 6, 2 and 3
• 8 is a whole number greater than one, evenly divisible by 1, 8, 2 and 4

Look back at the chart above and notice how all the figures not enlarged/highlighted represent the composite numbers to 100 (with the exception of 1 which is neither prime nor composite).

## A quick reminder of how prime and composite numbers differ

Are you now confident you can tell the difference between prime and composite numbers?

Okay, it's time to move on - next up prime factorization.