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Prime numbers
A prime number has exactly two divisors: 1 and itself.
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2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47.
2 is the only even prime. 1 is not prime.
How to test a number
Try dividing by the primes 2, 3, 5, 7 … up to the square root of the number. If none divides it evenly, it is prime.
Try it yourself
- Is 29 prime? = ?
- Is 51 prime? = ?
- Is 37 prime? = ?
- Is 49 prime? = ?
- Is 1 prime? = ?
- Is 43 prime? = ?
Show answers
- Is 29 prime? = Yes
- Is 51 prime? = No (3 × 17)
- Is 37 prime? = Yes
- Is 49 prime? = No (7 × 7)
- Is 1 prime? = No
- Is 43 prime? = Yes
Frequently asked questions
Why is 1 not prime?
A prime needs exactly two different divisors; 1 has only one.