Python Program to Check Prime Number

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.")
    print(f"{num} is not a prime number.")

How the Program Works

  1. 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.
  1. The user inputs a number to be checked.
  2. The program calls the is_prime function and prints whether the number is prime or not.


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!