An algorithm used for finding all prime integers less than some positive number n. First create a list of all positive integers from 2 to n. Then, letting p be the first number in the list, repeatedly count up in increments of p and mark each number on that index excluding p itself (2p, 3p, 4p, and so on). p will then take the value of the next unmarked number. After iterating through the whole list, all the numbers that are not marked at the end will be prime.
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