In this article, we will learn about how to write python program to find sum of N natural numbers using recursion.

Getting Started

The task is to find the sum of N natural numbers using recursion. For example,

If N = 10, then output should be 55 because sum of first N natural numbers in 55 i.e. 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 = 55.

If N = 5, then output should be 15 because 1 + 2 + 3 + 4 + 5 = 15.

Using Recursion

We can write program to find sum of N natural numbers recursively too. It’s just a recursive approach of for loop program.

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

# Get user input for N
n = int(input("Enter a positive integer N: "))
result = sum_of_n_numbers(n)
print(f"The sum of the first {n} natural numbers is: {result}")

Here,

• sum_of_n_numbers method is getting called recursively until the last value 1.
• In the last call, this method will return 1.
• After that, second last call will be executed. In this call, 1 + 2 will be returned.
• Subsequently, all method calls will be executed and we will get sum of n numbers.

Output:

Enter a positive integer N: 
4
The sum of the first 4 natural numbers is: 10

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That’s how you can write python program to find sum of N natural numbers using recursion.