Yes, 43 is a prime number. Its only factors are 1 and 43.
A number is prime if no smaller prime up to its square root divides it. The square root of 43 is about 6.56, so it is enough to test the primes 2, 3 and 5.
| Divide by | Remainder | Divides evenly? |
|---|---|---|
| 2 | 1 | No |
| 3 | 1 | No |
| 5 | 3 | No |
None of them divides 43 evenly, so 43 is prime.
| Number | Prime? |
|---|---|
| 39 | No, 3 × 13 |
| 40 | No, 2 × 2 × 2 × 5 |
| 41 | Yes |
| 42 | No, 2 × 3 × 7 |
| 44 | No, 2 × 2 × 11 |
| 45 | No, 3 × 3 × 5 |
| 46 | No, 2 × 23 |
| 47 | Yes |
More about 43: factors of 43 · 43 squared · square root of 43 · 43 in binary · 43 in Roman numerals.
Another number? Use the prime number checker for any value, or see the list of prime numbers.