Primes between two numbers
Find all prime numbers in any range. Lists every prime between your start and end values.
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Sieve of Eratosthenes
The classic algorithm for finding primes: list all numbers, then cross out multiples of 2, then 3, then 5, then 7... The unmarked numbers that remain are prime.
How many primes are there?
Primes between 1–100: 25. Between 1–1000: 168. Between 1–10,000: 1,229. Primes are infinite — Euclid proved this around 300 BC.
Prime density
About 1 in every ln(n) numbers near n is prime. Near 100, roughly 1 in 4.6 numbers is prime. Near 1,000,000, roughly 1 in 13.8.
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