Sieve of Eratosthenes
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Python Basics · Functions →
Sieve of Eratosthenes
The Greek mathematician Eratosthenes found primes without dividing anything: write down the numbers, then cross out the multiples of each prime.
[True] * (n + 1) makes a list of n + 1 True values, one for each number from 0 to n. Mark 0 and 1 as not prime. Then, for each p still marked True, set every multiple of p from p * p onwards to False. The numbers still marked True at the end are the primes.
Write primes_up_to(n) that returns every prime number from 2 to n in order, using the sieve of Eratosthenes. primes_up_to(10) is [2, 3, 5, 7].
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