Is 43 a prime number?
43 is a prime number. Here is how to check it, one division at a time.
The answer
Yes. 43 is a prime number: its only factors are 1 and 43.
How to check that 43 is prime
Try dividing 43 by the prime numbers, starting with 2. You only need primes: if 4 went into 43, then 2 would too.
- 43 ÷ 2 = 21 remainder 1, so 2 is not a factor.
- 43 ÷ 3 = 14 remainder 1, so 3 is not a factor.
- 43 ÷ 5 = 8 remainder 3, so 5 is not a factor.
Stop at 7: 7 × 7 = 49, which is more than 43. Any factor bigger than that would need a partner smaller than 7, and you have already tried those. So 43 is prime.
Where 43 comes among the primes
43 is the 14th prime number. The prime just before it is 41.
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 43
- 43 is not in any times table from 2 to 12. The answers either side of it are 42 (6 × 7 and 7 × 6) and 44 (4 × 11 and 11 × 4).
- The nearest square number is 49 (7 × 7), 6 above it.
- Two prime numbers with a difference of 4 are called cousin primes. 43 has one cousin prime: 47.
43 at a glance
Optional extra number facts:
- In words
- forty-three
- In Roman numerals
- XLIII
- Odd or even
- Odd: it ends in 3
- Its factors add up to
- 44, or 1 without 43 itself. 43 is deficient: Deficient means this sum is less than the number.
Related pages
More numbers
Questions parents ask
Is 43 one of a pair of twin primes?
Yes. Twin primes are two primes 2 apart, and 43 pairs with 41.
What is the next prime number after 43?
47, which is 4 more than 43. Every number in between has a factor other than 1 and itself.
What is 43 × 43?
43 × 43 = 1849. The square of a prime has exactly three factors: 1, 43 and 1849.
Continue your number practice
Explore the diagnostic for another set of practice questions.