Is 79 a prime number?
79 is a prime number. Here is how to check it, one division at a time.
The answer
Yes. 79 is a prime number: its only factors are 1 and 79.
How to check that 79 is prime
Try dividing 79 by the prime numbers, starting with 2. You only need primes: if 4 went into 79, then 2 would too.
- 79 ÷ 2 = 39 remainder 1, so 2 is not a factor.
- 79 ÷ 3 = 26 remainder 1, so 3 is not a factor.
- 79 ÷ 5 = 15 remainder 4, so 5 is not a factor.
- 79 ÷ 7 = 11 remainder 2, so 7 is not a factor.
Stop at 11: 11 × 11 = 121, which is more than 79. Any factor bigger than that would need a partner smaller than 11, and you have already tried those. So 79 is prime.
Where 79 comes among the primes
79 is the 22nd prime number. The prime just before it is 73.
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 79
- 79 is not in any times table from 2 to 12. The answers either side of it are 77 (7 × 11 and 11 × 7) and 80 (8 × 10 and 10 × 8).
- The nearest square number is 81 (9 × 9), 2 above it.
- Two prime numbers with a difference of 4 are called cousin primes. 79 has one cousin prime: 83.
79 at a glance
Optional extra number facts:
- In words
- seventy-nine
- In Roman numerals
- LXXIX
- Odd or even
- Odd: it ends in 9
- Its factors add up to
- 80, or 1 without 79 itself. 79 is deficient: Deficient means this sum is less than the number.
Related pages
More numbers
Questions parents ask
Is 79 one of a pair of twin primes?
No. Twin primes are two primes 2 apart, such as 11 and 13. Neither 77 nor 81 is prime, so 79 has no twin.
What is the next prime number after 79?
83, which is 4 more than 79. Every number in between has a factor other than 1 and itself.
What is 79 × 79?
79 × 79 = 6241. The square of a prime has exactly three factors: 1, 79 and 6241.
Continue your number practice
Explore the diagnostic for another set of practice questions.