Is 3991 a prime number?
No, 3991 is not a prime number. It is divisible by 13: 3991 = 13 × 307.
Is 3991 prime?
Pick any whole number from 1 to 10,000.
How to work it out
- 1
A prime number has exactly two factors: 1 and itself.
- 2
It is enough to test the primes up to √3991 ≈ 63.17. If none of them divides 3991, it is prime.
- 3
13 divides 3991 exactly, so it is not prime. Its prime factorisation is
LaTeX source of the formulas on this page
\[ 3991 = 13 \times 307 \]
Testing 3991 by the primes up to its square root
| Prime | Division | Result |
|---|---|---|
| 2 | 3991 ÷ 2 | leaves 1 |
| 3 | 3991 ÷ 3 | leaves 1 |
| 5 | 3991 ÷ 5 | leaves 1 |
| 7 | 3991 ÷ 7 | leaves 1 |
| 11 | 3991 ÷ 11 | leaves 9 |
| 13 | 3991 ÷ 13 | divides exactly (307) |
| 17 | 3991 ÷ 17 | leaves 13 |
| 19 | 3991 ÷ 19 | leaves 1 |
| 23 | 3991 ÷ 23 | leaves 12 |
| 29 | 3991 ÷ 29 | leaves 18 |
| 31 | 3991 ÷ 31 | leaves 23 |
| 37 | 3991 ÷ 37 | leaves 32 |
Questions
Is 3991 a prime number?
No, 3991 is not a prime number. It is divisible by 13: 3991 = 13 × 307.
What is the next prime after 3991?
4001.
What is the prime number before 3991?
3989.
What are the factors of 3991?
1, 13, 307, 3991.