🚀 Day 29/150 – Sum of First N Natural Numbers in Python

Finding the sum of first N natural numbers is a classic beginner problem that helps you understand loops, formulas, and basic arithmetic in Python.

👉 Natural numbers start from 1
Examples: 1, 2, 3, 4, 5...

If N = 5

Sum = 1 + 2 + 3 + 4 + 5 = 15

Let’s explore different methods 👇

🔹 Method 1 – Using for Loop

The most common approach.

n = 5
total = 0

for i in range(1, n + 1):
    total += i

print("Sum:", total)

✅ Explanation:

• Start total = 0
• Add each number from 1 to N
• Print final sum

🔹 Method 2 – Using Formula

Fastest mathematical solution.

n = 5

total = n * (n + 1) // 2

print("Sum:", total)

✅ Explanation:

Formula:

$$\text{Sum} = \frac{n(n+1)}{2}$$

• Very efficient
• No loop required

🔹 Method 3 – Taking User Input

Interactive version.

n = int(input("Enter a number: "))

total = n * (n + 1) // 2

print("Sum:", total)


🔹 Method 4 – Using while Loop
Condition-based approach.
n = 5
i = 1
total = 0

while i <= n:
    total += i
    i += 1

print("Sum:", total)


































🎯 Final Thoughts

Use formula for best performance ⚡

Use loop methods for learning logic 🧠