How_To_Be_Good_At_Math

NUMBERS • PRIME NUMBERS 33

Prime numbers

up to 100

This table shows all the prime

numbers from 1 to 100.

Prime numbers

are shaded

dark purple

2 is the only even

prime. All other even

numbers can be divided

by 2 so are not prime

1 is not a prime number

because it doesn’t have two

different factors – 1 and itself

are the same number!

Non-primes

are shaded

pale purple

The largest prime

The ancient Greek

mathematician Euclid worked

out that we can never know

the largest possible prime

number. The largest prime we

currently know is more than

22 million digits long! It’s

written like this:

Prime or not prime?

There’s a simple trick we can use to check whether a number

is prime – just follow the steps on this chart:

CAN YOU DIVIDE THIS NUMBER

EXACTLY BY 2, 3, 5, OR 7?

PICK A WHOLE NUMBER

FROM 2 TO 100

IT’S A PRIME

NO YES

IT’S NOT A PRIME

2

74 207 281

−1

This means “multiply 2

by itself 74 207 281

times, then subtract 1”

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

61 62 63 64 65 66 67 68 69 70

91 92 93 94 95 96 97 98 99 100

81 82 83 84 85 86 87 88 89 90

71 72 73 74 75 76 77 78 79 80

51 52 53 54 55 56 57 58 59 60

REAL WORLD MATHS

032_033_Prime_Numbers.indd 33 29/02/2016 14:08