Screening method
The screening method is also called the screening method. The specific method is: first arrange the N natural numbers in order. 1 is not a prime number, nor is it a composite number, so it should be crossed out. The second number 2 is the prime number left, and all the numbers after 2 that are divisible by 2 are crossed out. The first number that is not crossed out after 2 is 3. Leave 3 and cross out all the numbers after 3 that are divisible by 3. The first number that is not crossed out after 3 is 5. Leave 5 and cross out all the numbers after 5 that are divisible by 5. If you keep doing this, all composite numbers that do not exceed N will be screened out, leaving all prime numbers that do not exceed N. Because the Greeks wrote the numbers on the wax-coated board. Every time a number was crossed out, a small dot was written on it. After the work of searching for prime numbers was completed, these small dots were like a sieve, so they put Ella Tostellini's method is called "Elatostellini Sieve", or "sieve method" for short. (Another explanation is that the numbers at that time were written on papyrus. Every time a number was crossed out, the number was dug out. After the work of seeking prime numbers was completed, these many small holes were like a sieve.)