Python Programs | IT Developer
IT Developer

Python Programs

Share with a Friend
Previous
HOME
Next

Python Programs - Looping Statements

Find the sum of first n natural numbers - Python Program

Example 1 :

Python 
#  Sum of first n natural numbers

n = int(input("Enter n: "))
total = 0

for i in range(1, n + 1):
    total += i

print(f"Sum of first {n} natural numbers = {total}")

Output

 
OUTPUT  :
Enter n: 10
Sum of first 10 natural numbers = 55

Example 2 : Advanced Program

Method 1: Using the Formula

The sum of the first 'n' natural numbers can be calculated directly using the formula: n * (n + 1) / 2. This is the most efficient method as it involves a constant number of operations regardless of the value of 'n'. 

Python 
def sum_of_natural_numbers_formula(n):
    """
    Calculates the sum of the first n natural numbers using the mathematical formula.
    """
    if n < 0:
        return "Input must be a non-negative integer."
    return n * (n + 1) // 2  # Use // for integer division

# Get input from the user
try:
    num = int(input("Enter a positive integer (n): "))
    result = sum_of_natural_numbers_formula(num)
    print(f"The sum of the first {num} natural numbers is: {result}")
except ValueError:
    print("Invalid input. Please enter an integer.")

Output

 
OUTPUT  :
Enter a positive integer (n): 10
The sum of the first 10 natural numbers is: 55

Example 3 : Advanced Program

Method 2: Using a Loop

This method involves iterating from 1 to 'n' and accumulating the sum in a variable.

 

Python 
def sum_of_natural_numbers_loop(n):
    """
    Calculates the sum of the first n natural numbers using a for loop.
    """
    if n < 0:
        return "Input must be a non-negative integer."
    total_sum = 0
    for i in range(1, n + 1):
        total_sum += i
    return total_sum

# Get input from the user
try:
    num = int(input("Enter a positive integer (n): "))
    result = sum_of_natural_numbers_loop(num)
    print(f"The sum of the first {num} natural numbers is: {result}")
except ValueError:
    print("Invalid input. Please enter an integer.")

Output

 
OUTPUT  :
Enter a positive integer (n): 10
The sum of the first 10 natural numbers is: 55
Previous
Next