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1. Count Digits Recursively2. Reverse Number Recursively3. Check Palindrome Recursively4. Product of Digits Recursively5. GCD Recursively6. Convert Number to Binary Recursively7. Print Digits in Words8. Sum of First N Even Numbers Recursively9. Sum of First N Odd Numbers Recursively10. nCr Recursively (Pascal Formula)

Sum of First N Even Numbers Recursively

Calculate sum of first n even numbers recursively.

IntermediatePhase 3 - Level 2: Advanced RecursionExample 8 of 10
sum-of-first-n-even-numbers-recursively.py
1def sum_even(n):
2    # Base case
3    if n == 0:
4        return 0
5    
6    # Recursive case
7    # nth even number is 2*n
8    return (2 * n) + sum_even(n - 1)
9

10# Test
11n = int(input("Enter n: "))
12result = sum_even(n)
13print(f"Sum of first {n} even numbers: {result}")

Output

Enter n: 5
Sum of first 5 even numbers: 30

What's going on

Nth even number is 2*n.

Key Concepts:

Base case: sum(0) = 0
Nth even number = 2*n
Add current even number to sum of previous

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