Prime numbers
python implementation of the sieve of erastosthenes
Erastosthenes of Cyrene discovered that one can find all prime numbers by writing down a list of integers from 2(the first prime number) up to an arbitrary number, then deleting all multiples of 2(which are by definition not prime numbers), find the next undeleted number, which is 3, delete all its multiples, find the next number after that, 5, delete all ts multiples and so on.
All numbers that remain are prime numbers.