Python Program to Print Prime Numbers

Welcome to our guide on writing a Python program to print prime numbers!

In this tutorial, we’ll walk through the process of creating a simple yet efficient Python program that generates prime numbers.

Prime numbers are natural numbers greater than 1 that have no positive divisors other than 1 and themselves.

They are essential in various mathematical applications and algorithms.

Creating a program to print prime numbers is a fundamental exercise that demonstrates key concepts in programming, such as loops, conditionals, and algorithmic efficiency.

Before diving into the code, let’s briefly understand prime numbers.

A prime number is a whole number greater than 1 that is divisible only by 1 and itself.

For example, 2, 3, 5, 7, 11, and 13 are prime numbers.

Naive Approach to Finding Prime Numbers

One of the simplest approaches to finding prime numbers is the brute-force method.

We iterate through each number from 2 to the given limit and check if it is divisible by any number other than 1 and itself.

If not, the number is prime.

Here’s the basic algorithm:

1. Start from 2 and go up to the desired limit.
2. For each number, check if it’s divisible by any number from 2 to the square root of the number.
3. If the number is not divisible by any other number, it’s prime.

Python Program to Print Prime Numbers

Let’s now implement the Python program to print prime numbers using the brute-force method.

# Function to check if a number is prime
def is_prime(num):
    if num <= 1:
        return False
    for i in range(2, int(num**0.5) + 1):
        if num % i == 0:
            return False
    return True

# Function to print prime numbers up to a given limit
def print_primes(limit):
    primes = []
    for num in range(2, limit + 1):
        if is_prime(num):
            primes.append(num)
    return primes

# Main function
limit = int(input("Enter the upper limit to find prime numbers: "))
prime_numbers = print_primes(limit)
print("Prime numbers up to", limit, "are:", prime_numbers)

In the above code:

• The is_prime() function checks if a given number is prime by iterating from 2 to the square root of the number and checking for divisibility.
• The print_primes() function generates a list of prime numbers up to a given limit using the is_prime() function.
• Then we take user input for the upper limit and print the prime numbers up to that limit.

Testing the Python Program to Print Prime Numbers

Let’s test our program with a few examples:

Example 1: Printing Prime Numbers up to 20

limit = 20
prime_numbers = print_primes(limit)
print("Prime numbers up to", limit, "are:", prime_numbers)

Output

Example 2: Printing Prime Numbers up to 50

limit = 50
prime_numbers = print_primes(limit)
print("Prime numbers up to", limit, "are:", prime_numbers)

Output

Optimizing the Algorithm

The brute-force method works fine for small limits but becomes inefficient for larger limits.

For larger ranges, we can use more sophisticated algorithms like the Sieve of Eratosthenes.

In this tutorial, we’ve explored how to write a Python program to print prime numbers using a brute-force method.

We’ve discussed the concept of prime numbers, implemented the program step by step, and tested it with examples.

Additionally, we’ve touched upon the efficiency of the algorithm and potential optimizations.

Feel free to experiment with the code and explore other prime number generation algorithms.

Prime numbers have applications in cryptography, number theory, and various fields of computer science.

If you have any questions or suggestions, please leave a comment below!