Factors of 45
Every whole number that divides 45 exactly, the factor pairs, and how to find them yourself.
The answer
The factors of 45 are 1, 3, 5, 9, 15 and 45.
Factor pairs of 45
| Pair | Makes |
|---|---|
| 1 × 45 | 45 |
| 3 × 15 | 45 |
| 5 × 9 | 45 |
Prime factors of 45
- Prime factorisation
- 45 = 3 × 3 × 5 (3² × 5)
- Reading index form
- A small raised number tells you how many times to use that factor. For example, 2³ means 2 × 2 × 2.
- Is 45 prime?
- No. It has 6 factors, not just 1 and 45.
- Is 45 a square number?
- No. 6 × 6 = 36 and 7 × 7 = 49, so 45 falls between two square numbers.
How to find the factors of 45
45 is odd, so every even number you try will fail. Its digits add up to 9, a multiple of 9, so 3 and 9 are factors. It ends in 5, so 5 is a factor. Work up from 1 to 6, and write down both numbers in every pair you find.
- 45 ÷ 1 = 45, so 1 × 45 is a pair.
- 2 does not go into 45 exactly.
- 45 ÷ 3 = 15, so 3 × 15 is a pair.
- 4 does not go into 45 exactly.
- 45 ÷ 5 = 9, so 5 × 9 is a pair.
- 6 does not go into 45 exactly.
Stop at 7: 7 × 7 = 49, which is more than 45. The next pair you would find is 9 × 5, which is 5 × 9 turned round, so you already have every pair.
45 in the times tables
3 × 15 = 45 and 5 × 9 = 45. Practise the 5 times table, 9 times table and 15 times table.
More numbers
Check whether 45 is prime.
Questions parents ask
What is the largest factor of 45, apart from 45 itself?
15. Divide 45 by its smallest factor above 1, which is 3: 45 ÷ 3 = 15.
What do the factors of 45 add up to?
78. Leaving out 45 itself, they add up to 33, which is less than 45, so 45 is called a deficient number.
Which number after 45 has the same number of factors?
50. Like 45, it has exactly 6 factors.
Continue your number practice
Explore the diagnostic for another set of practice questions.