# Python Program to check if a Number is Prime or not

|In this Python example, we will discuss how to check if any given number is a prime number or not. Let’s begin.

Table of Contents

## 1. What is a Prime Number?

A prime number is a number that can only be divided by itself and 1 without remainders. A prime number is a number greater than 1 with only two factors – themselves and 1.

According to Wikipedia

EXAMPLE:Input :13Output :13 is a Prime NumberExplanation :13 has only two factors; 1 and itselfInput :10Output :10 is not a Prime NumberExplanation :10 has more than two factors; 1, 2, 5 and itself

Some of the topics which will be helpful for understanding the program implementation better are:

## 2. Basic Program to Check Prime Number

- In this method, we will check if the input value is 1 or not; if it is more than 1 then only we will proceed further.
- Using a for loop, we will divide the input number from 2 to input-1. If any factor lies in that
`range`

, then the input number is not prime, and we will break the loop. - If any factor does not lie in that
`range`

, then we can say that the input number is a prime number.

Let’s implement the code and see how it works.

#Python Program to Check if a number is prime or not def check_prime(n): if n > 1: for i in range(2, n): if (n % i) == 0: return True break else: return "Input number must be greater than 1" n = int(input("Enter the number to check if it is Prime: ")) if check_prime(n): print(n, "is not a Prime Number.") else: print(n, "is a Prime Number")

OutputEnter the number to check if it is Prime: 12 12 is not a Prime Number.

**There is a possibility or the improvement in the above code**

- We can also find a number that the given number is prime or not using the loop with a
`range`

from`2`

to`n/2`

; divide the input number from 2 to n/2. - If any factor lies in that range, then the input number is not prime, and we will break the loop.
- If any factor does not lie in that range, then we can say that the input number is a prime number.

#Python Program to Check if a number is prime or not using half range n = int(input("Enter the number to check if it is Prime or not: ")) if n > 1: for i in range(2, int(n/2)+1): if n % i == 0: print(n, "is not a prime number") break else: print(n, "is a prime number") else: print(n, "is not a prime number")

## 3. Check if Number is Prime or not using sqrt

In this method, we take the help of the `sqrt`

function inside the `math module`

.

Rather than checking the loop condition till n, we can check it up to `√n`

. The reason for doing this is because any input number n will have larger factors as multiple of smaller factors that are already checked.

Let’s implement and find out the working of the code.

#Python Program to Check if n umber is prime or not using sqrt from math import sqrt n = int(input("Enter the number to check for Prime: ")) if n > 1: for i in range(2, int(sqrt(n)) + 1): if (n % i == 0): print("This is Not a Prime Number") break else: print("This is a Prime Number") else: print("Invalid Input")

OutputEnter the number to check for Prime: 31 This is a Prime Number

## 4. Conclusion

In this article, we have covered the Python program to check whether a given number is Prime or not using a basic for loop method and sqrt function.

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