(nb)
| 12 | # - 1 is not a prime. |
| 13 | # - All primes except 2 are odd. |
| 14 | def isPrime(nb): |
| 15 | if nb == 1: |
| 16 | return False |
| 17 | elif nb == 2 or nb == 3: |
| 18 | return True |
| 19 | elif isEven(nb): |
| 20 | return False |
| 21 | |
| 22 | # square root of `nb` rounded to the greatest integer `root` so that: |
| 23 | # root * root <= nb |
| 24 | root = math.ceil(math.sqrt(nb)) |
| 25 | |
| 26 | for f in range(3, root + 1, 2): |
| 27 | if nb % f == 0: |
| 28 | return False |
| 29 | return True |
| 30 | |
| 31 | |
| 32 | # `count` starts to 1 because we already know that 2 is prime |