Prime numbers are numbers can only be divided by itself and 1. They are greater than 0. In this text, we will see how to test whether a number is a prime number or not. Furthermore, we will find prime numbers up to N. ( N is a number entered by user. )

For example, 2 can be divided by 2 and 1. So it is a prime number.

Prime numbers: 2, 3, 5, 7, 11 ,13, 17, 19, …

**How to test a number ?**

“A” is a positive number greater than 1. Let X be a number different than number A and 1. If we can find such a number divide A with remainder 0, A is not a prime number.

- X can be preferred prime numbers less than square root of A. This make our program slightly faster.

**A** : 29 and **Square root of A** : 5.385164

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