Is 27 a prime number?
27 is not a prime number. Here is a way to check 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 repeated primes written as powers, that is 3³. A small raised number tells you how many times to use that factor: for example, 2³ means 2 × 2 × 2.
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
Optional extra number facts:
- 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. 27 is deficient: Deficient means this sum is less than the 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.
Continue your number practice
Explore the diagnostic for another set of practice questions.