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Program for Sum of n Natural Numbers in Python (Code Examples)

In programming, efficiency and elegance go hand in hand. When it comes to calculating the sum of n natural numbers in Python, this programming language offers various approaches, each with its own advantages and nuances. 

In this post, we will explore different techniques to tackle this simple task. From traditional methods like using loops to more advanced approaches like utilizing mathematical formulas, we leave no stone unturned in our exploration. 

Finding the sum of natural numbers in Python is useful whether you are a beginner seeking to grasp the basics or a seasoned programmer searching for new insights.

Through a series of code examples with simple explanations, we will show you how to calculate the sum of n natural numbers using a variety of Python concepts. 

Sum of n Numbers in Python Using for loop

Code

# Find sum of n natural numbers in Python with for loop

def calculate_sum(n):
    sum = 0

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

    return sum

# Example usage
num = int(input("Enter a number: "))

total_sum = calculate_sum(num)
print(f"The sum of the first {num} natural numbers is: {total_sum}")

Output

Enter a number: 20
The sum of the first 20 natural numbers is: 210

Explanation

  • We define a function calculate_sum that takes a parameter n. We initialize the variable sum to 0, which will store the cumulative sum of the numbers.

  • We use a for loop to iterate from 1 to n (inclusive). In each iteration, we add the current value of i to the sum variable using the += operator.

  • After the loop finishes, we return the final value of sum as the result.

  • In the example, we prompt the user to enter a number using the input function and convert it to an integer using int(). 

  • We then call the calculate_sum function with the entered number as the argument and store the result in the variable total_sum. Finally, we display the calculated sum to the user.

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Sum of n Natural Numbers in Python Using while loop

Code

# Sum of first n natural numbers in Python with while loop

def calculate_sum(n):
    sum = 0
    i = 1

    while i <= n:
        sum += i
        i += 1

    return sum

# Example usage
num = int(input("Enter a number: "))

total_sum = calculate_sum(num)
print(f"The sum of the first {num} natural numbers is: {total_sum}")

Output

Enter a number: 30
The sum of the first 30 natural numbers is: 465

Explanation

  • We define the calculate_sum function that takes a parameter n. We initialize the variable sum to 0, which will store the cumulative sum of the numbers. Additionally, we initialize i to 1, which represents the current number being added to the sum.

  • We use a while loop with the condition i <= n to iterate until the value of i reaches n. Inside the loop, we add the current value of i to the sum variable using the += operator. After that, we increment i by 1 using i += 1.

  • The loop continues until the value of i becomes greater than n. Once the loop finishes, we return the final value of sum as the result.

  • In the example part, we prompt the user to enter a number using the input function and convert it to an integer using int(). We then call the calculate_sum function with the entered number as the argument and store the result in the variable total_sum. 

  • Finally, we display the calculated sum to the user.

Sum of n Natural Numbers in Python Using Recursion

Code

# Sum of n natural numbers in Python with recursion

def calculate_sum(n):
    if n == 1:
        return 1
    else:
        return n + calculate_sum(n - 1)

# Example usage
num = int(input("Enter a number: "))

total_sum = calculate_sum(num)
print(f"The sum of the first {num} natural numbers is: {total_sum}")

Output

Enter a number: 10
The sum of the first 10 natural numbers is: 55

Explanation

  • We define a recursive function called calculate_sum that takes a parameter n. Inside the function, we have a base case that checks if n is equal to 1. If n is 1, we return 1, as the sum of the first natural number is 1.

  • For any other value of n, we make a recursive call to calculate_sum with n - 1 as the argument and add n to the result of the recursive call. This way, we break down the problem of calculating the sum of n natural numbers in Python into smaller subproblems until we reach the base case.

  • The recursive function keeps calling itself with smaller values of n until it reaches the base case, and then it starts returning the results back up the call stack to calculate the final sum.

  • In the example part, we prompt the user to enter a number using the input function and convert it to an integer using int(). We then call the calculate_sum function with the entered number as the argument and store the result in the variable total_sum. 

  • Finally, we print the calculated sum and show it.

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