Is 11 a prime number?
11 is a prime number. Here is how to check it, one division at a time.
The answer
Yes. 11 is a prime number: its only factors are 1 and 11.
How to check that 11 is prime
Try dividing 11 by the prime numbers, starting with 2. You only need primes: if 4 went into 11, then 2 would too.
- 11 ÷ 2 = 5 remainder 1, so 2 is not a factor.
- 11 ÷ 3 = 3 remainder 2, so 3 is not a factor.
Stop at 5: 5 × 5 = 25, which is more than 11. Any factor bigger than that would need a partner smaller than 5, and you have already tried those. So 11 is prime.
Where 11 comes among the primes
11 is the 5th prime number. The prime just before it is 7.
There are 25 prime numbers up to 100: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89 and 97.
Around 11
- 11 is in only one times table, its own, as 11 × 1. The next answer in it is 11 × 2 = 22.
- The nearest square number is 9 (3 × 3), 2 below it.
- Primes 4 apart are called cousin primes, and 11 has one cousin: 7.
11 at a glance
- In words
- eleven
- In Roman numerals
- XI
- Odd or even
- Odd: it ends in 1
- Its factors add up to
- 12, or 1 without 11 itself, which makes 11 a deficient number
Related pages
More numbers
Questions parents ask
Is 11 one of a pair of twin primes?
Yes. Twin primes are two primes 2 apart, and 11 pairs with 13.
What is the next prime number after 11?
13, which is 2 more than 11. Every number in between has a factor other than 1 and itself.
What is 11 × 11?
11 × 11 = 121. The square of a prime has exactly three factors: 1, 11 and 121.
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.