How to judge primes by php

This article will explain in detail how php judges primes. The editor thinks it is very practical, so I share it with you as a reference. I hope you can get something after reading this article.

1. The easiest way is to find it according to the definition of prime.

A prime can only be divisible by 1 and itself, that is, it can only be divisible twice.

So we use a loop to remove N from every natural number greater than 1 and less than or equal to N, and count the number of times divisible. If the number is greater than 2, it is not a prime; if it is equal to 2, it is a prime.

2. Divide a number from 2 to sqrt (this number). If it is divisible, it shows that the number is not a prime number, on the contrary, it is a prime number.

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