Is 9 a prime number?
9 is not a prime number. Here is the quickest way to see it.
The answer
No. 9 is not a prime number: 3 × 3 = 9.
How to see that 9 is not prime
9 is in the 3 times table, so 3 is a factor as well as 1 and 9.
9 has only three factors, 1, 3 and 9: just one more than a prime has, which is still enough to rule it out.
Split 9 into prime factors
9 is 3 × 3: the same prime twice, so its factor tree stops after one split.
9 in the times tables
9 turns up in 2 different times tables, the 3 and 9: 3 × 3 and 9 × 1.
Quick checks that catch 9
- 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.
9 at a glance
- In words
- nine
- In Roman numerals
- IX
- Odd or even
- Odd: it ends in 9
- Square number
- 3 × 3 = 9
- Its factors add up to
- 13, or 4 without 9 itself, which makes 9 a deficient number
The numbers either side of 9
- 8 is not prime. 8 is in the 2 times table, so 2 is a factor as well as 1 and 8. Check 8 in full
- 10 is not prime. 10 is even, and every even number can be divided by 2, so 2 is a factor as well as 1 and 10. Check 10 in full
Related pages
More numbers
Questions parents ask
Which prime numbers are either side of 9?
7 below it and 11 above it, a gap of 4.
What is 9 squared?
9 × 9 = 81.
What is the smallest number with as many factors as 9?
4. It has 3 factors, the same as 9.
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.