Is 99 a prime number?
99 is not a prime number. Here is a way to check it.
The answer
No. 99 is not a prime number: 3 × 33 = 99.
How to see that 99 is not prime
Its digits add up to 9 + 9 = 18, which is a multiple of 3. That means 99 is a multiple of 3 too, so 3 is a factor.
99 has 6 factors (1, 3, 9, 11, 33 and 99), which make 3 factor pairs.
Split 99 into prime factors
Split off the smallest prime each time, and keep going until every part is prime:
- 99 = 3 × 33
- 99 = 3 × 3 × 11
With repeated primes written as powers, that is 3² × 11. A small raised number tells you how many times to use that factor: for example, 2³ means 2 × 2 × 2.
99 in the times tables
99 turns up in 2 different times tables, the 9 and 11: 9 × 11 and 11 × 9.
Quick checks that catch 99
- The digits add up to 18, which is in the 3 times table, so 3 goes in.
- The digit total, 18, is a multiple of 9, so 9 goes in.
- Its two digits match, and every two-digit number like that is in the 11 times table.
99 at a glance
Optional extra number facts:
- In words
- ninety-nine
- In Roman numerals
- XCIX
- Odd or even
- Odd: it ends in 9
- Its factors add up to
- 156, or 57 without 99 itself. 99 is deficient: Deficient means this sum is less than the number.
The numbers either side of 99
- 98 is not prime. 98 is even, and every even number can be divided by 2, so 2 is a factor as well as 1 and 98. Check 98 in full
- 100 is not prime. 100 is even, and every even number can be divided by 2, so 2 is a factor as well as 1 and 100. Check 100 in full
Related pages
More numbers
Questions parents ask
Which prime numbers are either side of 99?
97 below it and 101 above it, a gap of 4.
What is 99 squared?
99 × 99 = 9801.
What is the smallest number with as many factors as 99?
12. It has 6 factors, the same as 99.
Continue your number practice
Explore the diagnostic for another set of practice questions.