The Sieve of Erasthotenes is a very old algorithm to find by elimination the prime numbers up to a given integer N.

The manual process is so:

- write down the numbers from
**2**to N (say 100) - stripe the multiples of 2, except 2
- stripe the multiples of 3 not yet striped, except 3
- iterate the process for the next unstriped number
*k*: stripe the multiples of*k*not yet striped, except*k*. - continue until you get no more unstriped multiples before N

The unstriped remaining numbers are the numbers...