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1. Print 1 to N Recursively2. Factorial Using Recursion3. Print N to 1 Recursively4. Even Numbers 1-N Recursively5. Odd Numbers 1-N Recursively6. Sum of First N Natural Numbers Recursively7. Power x^n Recursively8. Nth Fibonacci Recursively9. Fibonacci Series Recursively10. Sum of Digits Recursively

Sum of First N Natural Numbers Recursively

Calculate sum of first n natural numbers recursively.

IntermediatePhase 3 - Level 1: Basic RecursionExample 6 of 10
sum-of-first-n-natural-numbers-recursively.py
1def sum_natural(n):
2    # Base case
3    if n == 0:
4        return 0
5    
6    # Recursive case
7    return n + sum_natural(n - 1)
8

9# Test
10n = int(input("Enter n: "))
11result = sum_natural(n)
12print(f"Sum: {result}")

Output

Enter n: 5
Sum: 15

What's going on

Sum(n) = n + Sum(n-1).

Key Concepts:

Base case: sum(0) = 0
Recursive: n + sum of n-1
Accumulate as recursion unwinds

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