In this post, we will learn **how to check prime numbers using Python** Programming language.

A** prime number** is a whole number greater than **1**, and has exactly two factors that is** 1** and the **number itself**. For example: 2, 3, 5, 7, 11, 13, 17, . . . and so on.

We will be using following approaches to check prime number:

- Using a flag Variable
- Using If-Else Statement

So, without further ado, let’s begin this tutorial.

**Python Program to Check Prime Number**

# Python Program to Check Prime Number num = int(input("Enter a number: ")) # defining a flag variable flag = 1 # Checking for factors for i in range(2, int (num/2)): if num % i == 0: flag = 0 break # Display output if flag == 1 and num >= 2: print(num, "is a prime number.") else: print(num, "is not a prime number.")

**Output 1**

```
Enter a number: 17
17 is a prime number.
```

**Output 2**

```
Enter a number: 25
25 is not a prime number.
```

**How Does This Program Work ?**

num = int(input("Enter a number: "))

The user is asked to enter a number. The entered number gets stored in the** num** named variable.

# defining a flag variable flag = 1

We define a variable named** flag**. Flag variable has assigned a value of **1**.

# Checking for factors for i in range(2, int (num/2)): if num % i == 0: flag = 0 break

Then, we check whether there is any factor of** num** greater than **2**. If yes, then the flag becomes **0** and the loop terminates.

if flag == 1 and num >= 2: print(num, "is a prime number.") else: print(num, "is not a prime number.")

If the value of the flag is **1** and **num >= 2**, then in this case the entered number doesn’t have any factors greater than **2** so, it is a prime number otherwise the entered number is not a prime number.

**Python Program to Check Prime Number Using If Else Statement**

# Python Program to Check Prime Number Using If-Else Statement num = int(input("Enter a number: ")) if num > 1: for i in range(2, num): if (num % i == 0): print(num, 'is not a prime number.') break else: print(num, 'is a prime number.') # If entered number is less than 1, then it is not a prime number else: print(num, "is not a prime number.")

**Output 1**

```
Enter a number: 13
13 is a prime number.
```

**Output 2**

```
Enter a number: 91
91 is not a prime number.
```

**Conclusion**

I hope after going through this post, you understand** how to check prime numbers using Python** Programming language.

If you have any doubt regarding the program, feel free to contact us in the comment section. We will be delighted to assist you.

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