Factors of 15
Every whole number that divides 15 exactly, the factor pairs, and how to find them yourself.
The answer
The factors of 15 are 1, 3, 5 and 15.
Factor pairs of 15
| Pair | Makes |
|---|---|
| 1 × 15 | 15 |
| 3 × 5 | 15 |
Prime factors of 15
- Prime factorisation
- 15 = 3 × 5
- Is 15 prime?
- No. It has 4 factors, not just 1 and 15.
- Is 15 a square number?
- No. 3 × 3 = 9 and 4 × 4 = 16, so 15 falls between two square numbers.
How to find the factors of 15
15 is odd, so every even number you try will fail. Its digits add up to 6, a multiple of 3, so 3 is a factor. It ends in 5, so 5 is a factor. Work up from 1 to 3, and write down both numbers in every pair you find.
- 15 ÷ 1 = 15, so 1 × 15 is a pair.
- 2 does not go into 15 exactly.
- 15 ÷ 3 = 5, so 3 × 5 is a pair.
Stop at 4: 4 × 4 = 16, which is more than 15. The next pair you would find is 5 × 3, which is 3 × 5 turned round, so you already have every pair.
15 in the times tables
3 × 5 = 15. Practise the 3 times table and 5 times table.
More numbers
Check whether 15 is prime.
Questions parents ask
What is the largest factor of 15, apart from 15 itself?
5. Divide 15 by its smallest factor above 1, which is 3: 15 ÷ 3 = 5.
What do the factors of 15 add up to?
24. Leaving out 15 itself, they add up to 9, which is less than 15, so 15 is called a deficient number.
Which number after 15 has the same number of factors?
21. Like 15, it has exactly 4 factors.
Continue your number practice
Explore the diagnostic for another set of practice questions.