Python Program to Find the Nth Prime Number

A prime number is a number that has exactly two factors: 1 and itself. The first few prime numbers are:

\[ 2,3,5,7,11,13,17,19,… \]

In this tutorial, we will write a Python program to find the Nth prime number, where N is a user-defined value.

Python Program to Find the Nth Prime Number

Method 1: Using a Loop and Prime Check

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

# Function to find the Nth prime number
def nth_prime(n):
    count = 0  # Count of prime numbers found
    num = 1  # Starting number to check
    while count < n:
        num += 1
        if is_prime(num):
            count += 1
    return num

# Taking user input
N = int(input("Enter the value of N: "))

# Finding and displaying the Nth prime number
print(f"The {N}th prime number is: {nth_prime(N)}")

Output

Enter the value of N: 5
The 5th prime number is: 11

Method 2: Using a Prime Number List

If you need to find multiple prime numbers efficiently, you can store primes in a list instead of checking each number individually.

def nth_prime(n):
    primes = [2]  # List of found primes
    num = 3  # Start checking from 3
    while len(primes) < n:
        if all(num % p != 0 for p in primes if p * p <= num):
            primes.append(num)
        num += 2  # Skip even numbers
    return primes[-1]

# Taking user input
N = int(input("Enter the value of N: "))

# Finding and displaying the Nth prime number
print(f"The {N}th prime number is: {nth_prime(N)}")

This method is faster because it avoids unnecessary calculations by checking divisibility with only stored primes.

Share your love
Subhankar Rakshit
Subhankar Rakshit

Hey there! I’m Subhankar Rakshit, the brains behind PySeek. I’m a Post Graduate in Computer Science. PySeek is where I channel my love for Python programming and share it with the world through engaging and informative blogs.

Articles: 201