Prime numbers play a crucial role in number theory and cryptography. They are positive integers greater than 1 that have no divisors other than 1 and themselves. In this blog, we’ll explore how to write a Python program to check if a given number is prime or not. Let’s dive in!

## Understanding Prime Numbers

A prime number is a positive integer that has exactly two distinct positive divisors: 1 and itself. For example, 2, 3, 5, 7, and 11 are prime numbers.

## The Python Program

Here’s a step-by-step guide on how to write a Python program to check if a number is prime:

```
def is_prime(number):
if number <= 1:
return False
if number <= 3:
return True
if number % 2 == 0 or number % 3 == 0:
return False
i = 5
while i * i <= number:
if number % i == 0 or number % (i + 2) == 0:
return False
i += 6
return True
# Input
num = int(input("Enter a number: "))
# Check if the number is prime
if is_prime(num):
print(f"{num} is a prime number.")
else:
print(f"{num} is not a prime number.")
```

## How the Program Works

- The
`is_prime`

function checks if a given number is prime or not using the following steps:

- If the number is less than or equal to 1, it’s not prime.
- If the number is 2 or 3, it’s prime.
- If the number is divisible by 2 or 3, it’s not prime.
- The function then checks divisibility by numbers of the form (6k \pm 1) up to the square root of the given number.

- The user inputs a number to be checked.
- The program calls the
`is_prime`

function and prints whether the number is prime or not.

## Conclusion

Writing a program to check for prime numbers is a fundamental exercise in programming. Understanding prime numbers and implementing algorithms to determine their primality enhances your problem-solving skills. This Python program demonstrates a straightforward approach to determine whether a number is prime, and you can further expand upon it by exploring different prime-checking algorithms or optimizing the code. Happy coding!