Exercise 4: Summation ∑

➕ Operators 🔂 Loops

Your Task

Write a program that asks the user for a number n, then computes and prints the sum:

$\sum_{i=1}^{n-1} i = 1 + 2 + 3 + \cdots + (n-1)$

Example: When n = 10:

$\sum_{i=1}^{9} i = 45$

Use a loop (or the formula (n-1) * n // 2) to compute it.

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Example Output

Enter n: 10
45