The Sieve of Eratosthenes is an efficient algorithm for computing the successive primes. Rendered informally, it is as follows:
1. Write down the successive “plurals”: 2, 3, 4, …
(a) Take the first number that is not circled or crossed out.
(b) Circle it.
(c) Cross out its proper multiples.
3. What is left (i.e. the circled numbers) are the successive prime numbers.