Is 100 a prime number?
100 is not a prime number. Here is the quickest way to see it.
The answer
No. 100 is not a prime number: 2 × 50 = 100.
How to see that 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.
100 has 9 factors (1, 2, 4, 5, 10, 20, 25, 50 and 100), which make 5 factor pairs.
Split 100 into prime factors
Split off the smallest prime each time, and keep going until every part is prime:
- 100 = 2 × 50
- 100 = 2 × 2 × 25
- 100 = 2 × 2 × 5 × 5
With the repeated primes written as powers, that is 2² × 5².
100 in the times tables
Just one of the 2 to 12 times tables has 100 in it: 10 × 10 = 100.
Quick checks that catch 100
- The last digit, 0, is even, so 2 goes in.
- Half of it is 50, which is still even, so 4 goes in.
- It ends in 0, so 5 goes in.
- It ends in 0, so 10 goes in.
100 at a glance
- In words
- one hundred
- In Roman numerals
- C
- Odd or even
- Even: it ends in 0
- Square number
- 10 × 10 = 100
- Multiple of 10
- 10 tens
- Its factors add up to
- 217, or 117 without 100 itself, which makes 100 an abundant number
The numbers either side of 100
- 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. Check 99 in full
- 101 is prime: 2, 3, 5 and 7 do not go into it, and 11 × 11 is already past 101.
Related pages
More numbers
Questions parents ask
Which prime numbers are either side of 100?
97 below it and 101 above it, a gap of 4.
What is 100 squared?
100 × 100 = 10000.
What is the smallest number with as many factors as 100?
36. It has 9 factors, the same as 100.
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.