Prime numbers are prime numbers, and the following are expressed as prime numbers
The screening method is also called screening method. The specific method is: first arrange N natural numbers in order.
1 is not a prime number, nor is it a composite number.Skip。（Combination numberRefers to a number in a natural number that can be divided by 1 and itself, except for 1 and itself. Contrary to prime number)
The second number 2 is the prime number left, andSkip all the numbers that can be divisible by 2 after 2。
The first number that has not been cut after 2 is 3. Leave 3 and thenSkip all the numbers that can be divisible by 3 after 3。
The first number that has not been cut after 3 is 5. Leave 5 and thenSkip all the numbers that can be divisible by 5 after 5。
Keep doing thisAll the combined numbers not exceeding N will be screened out, and all the prime numbers not exceeding N will be left behind.。
Because the Greeks wrote numbers on a waxed board, and every time a number was cut, they recorded small dots on it. After the work of seeking prime numbers was completed, these small dots were like a sieve, so the method of Elatostney was called "Elatostney sieve", abbreviated as "sieve method".
(Another explanation is that the number at that time was written on papyrus. Whenever a number was cut, the number was dug out. After the work of seeking prime numbers was completed, these small holes were like a sieve.)