Is 27 a prime number?
27 is not a prime number. Here is the quickest way to see it.
The answer
No. 27 is not a prime number: 3 × 9 = 27.
How to see that 27 is not prime
Its digits add up to 2 + 7 = 9, which is a multiple of 3. That means 27 is a multiple of 3 too, so 3 is a factor.
27 has four factors: 1 and 27, plus one pair in between, 3 and 9.
Split 27 into prime factors
Split off the smallest prime each time, and keep going until every part is prime:
- 27 = 3 × 9
- 27 = 3 × 3 × 3
With the repeated primes written as powers, that is 3³.
27 in the times tables
27 turns up in 2 different times tables, the 3 and 9: 3 × 9 and 9 × 3.
Quick checks that catch 27
- The digits add up to 9, which is in the 3 times table, so 3 goes in.
- The digit total, 9, is a multiple of 9, so 9 goes in.
27 at a glance
- In words
- twenty-seven
- In Roman numerals
- XXVII
- Odd or even
- Odd: it ends in 7
- Cube number
- 3 × 3 × 3 = 27
- Its factors add up to
- 40, or 13 without 27 itself, which makes 27 a deficient number
The numbers either side of 27
- 26 is not prime. 26 is even, and every even number can be divided by 2, so 2 is a factor as well as 1 and 26. Check 26 in full
- 28 is not prime. 28 is even, and every even number can be divided by 2, so 2 is a factor as well as 1 and 28. Check 28 in full
Turn the digits round
27 backwards is 72. 72 is not prime. 72 is even, and every even number can be divided by 2, so 2 is a factor as well as 1 and 72. Check 72 in full
Related pages
More numbers
Questions parents ask
Which prime numbers are either side of 27?
23 below it and 29 above it, a gap of 6.
What is 27 squared?
27 × 27 = 729.
What is the smallest number with as many factors as 27?
6. It has 4 factors, the same as 27.
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.