Is 57 a prime number?
57 is not a prime number. Here is the quickest way to see it.
The answer
No. 57 is not a prime number: 3 × 19 = 57.
How to see that 57 is not prime
Its digits add up to 5 + 7 = 12, which is a multiple of 3. That means 57 is a multiple of 3 too, so 3 is a factor.
57 has four factors: 1 and 57, plus one pair in between, 3 and 19.
Split 57 into prime factors
57 splits straight into two primes, 3 × 19, so its factor tree has only one branch.
57 in the times tables
No fact from the 2 to 12 times tables, up to × 12, makes 57. Its smallest pair, 3 × 19, needs the 19 times table, which goes past 12.
See the 19 times table, where 19 × 3 = 57 is one of the facts.
Quick checks that catch 57
- The digits add up to 12, which is in the 3 times table, so 3 goes in.
57 at a glance
- In words
- fifty-seven
- In Roman numerals
- LVII
- Odd or even
- Odd: it ends in 7
- Its factors add up to
- 80, or 23 without 57 itself, which makes 57 a deficient number
The numbers either side of 57
- 56 is not prime. 56 is even, and every even number can be divided by 2, so 2 is a factor as well as 1 and 56. Check 56 in full
- 58 is not prime. 58 is even, and every even number can be divided by 2, so 2 is a factor as well as 1 and 58. Check 58 in full
Turn the digits round
57 backwards is 75. 75 is not prime. Its digits add up to 7 + 5 = 12, which is a multiple of 3. That means 75 is a multiple of 3 too, so 3 is a factor. Check 75 in full
Related pages
More numbers
Questions parents ask
Which prime numbers are either side of 57?
53 below it and 59 above it, a gap of 6.
What is 57 squared?
57 × 57 = 3249.
What is the smallest number with as many factors as 57?
6. It has 4 factors, the same as 57.
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.