Python Functions

Python program to find the sum of natural numbers using recursion

Description: Write a Python program to find the sum of the first n natural numbers using recursion.

Rules and hints:

• A recursive function calls itself.
• Every recursive function needs a stopping (base) case.

Python program for the sum of natural numbers using recursion

def sum_to(n):
    if n == 0:
        return 0          # base case
    return n + sum_to(n - 1)

print(sum_to(5))
print(sum_to(10))

Output:

How it works

• sum_to(5) returns 5 + sum_to(4), and so on, down to sum_to(0) which returns 0.
• The results come back as 0, 1, 3, 6, 10 and 15.
• Without the base case the function would never stop and Python would raise a RecursionError.

See the Recursion section of Python Functions.