How to Find Sum of Natural Numbers Using Recursion in Python?

If a function calls itself, it is called a recursive function. In order to prevent it from falling in infinite loop, recursive call is place in a conditional statement.

Following program accepts a number as input from user and sends it as argument to rsum() function. It recursively calls itself by decrementing the argument each time till it reaches 1.

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

num = int(input("Enter a number: "))
ttl=rsum(num)
print("The sum is",ttl)

Sample run of above program prints sum o natural numbers upto input number

Enter a number: 10
The sum is 55