Factors of 51
Every whole number that divides 51 exactly, the factor pairs, and how to find them yourself.
The answer
The factors of 51 are 1, 3, 17 and 51.
Factor pairs of 51
| Pair | Makes |
|---|---|
| 1 × 51 | 51 |
| 3 × 17 | 51 |
Prime factors of 51
- Prime factorisation
- 51 = 3 × 17
- Is 51 prime?
- No. It has 4 factors, not just 1 and 51.
- Is 51 a square number?
- No. 7 × 7 = 49 and 8 × 8 = 64, so 51 falls between two square numbers.
How to find the factors of 51
51 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. Work up from 1 to 7, and write down both numbers in every pair you find.
- 51 ÷ 1 = 51, so 1 × 51 is a pair.
- 2 does not go into 51 exactly.
- 51 ÷ 3 = 17, so 3 × 17 is a pair.
- 4 does not go into 51 exactly.
- 5 does not go into 51 exactly.
- 6 does not go into 51 exactly.
- 7 does not go into 51 exactly.
Stop at 8: 8 × 8 = 64, which is more than 51. The next pair you would find is 17 × 3, which is 3 × 17 turned round, so you already have every pair.
51 in the times tables
3 × 17 = 51. Practise the 17 times table.
More numbers
Check whether 51 is prime.
Questions parents ask
What is the largest factor of 51, apart from 51 itself?
17. Divide 51 by its smallest factor above 1, which is 3: 51 ÷ 3 = 17.
What do the factors of 51 add up to?
72. Leaving out 51 itself, they add up to 21, which is less than 51, so 51 is called a deficient number.
Which number after 51 has the same number of factors?
55. Like 51, it has exactly 4 factors.
Number facts are the base of 11+ maths
Factors, multiples, primes and square numbers come up all over 11+ maths, from simplifying fractions to ratio. The free diagnostic checks maths, English and both kinds of reasoning, and shows what to practise next. No card is required.