Sum of n natural numbers

Given a number n, return the sum of the first n numbers. Return false for invalid inputs (non-number, negative numbers, or non-integer values).

Examples

Input: n = 5
Output: 15

Input: n = 0
Output: 0

Input: n = 1
Output: 1

Constraints

• Input must be a non-negative integer.
• Return false for invalid inputs.

Function Signature

function sumN(n) {
  // Your code here
}

Test Cases

• Base cases: 0, 1
• Small numbers: 2, 3, 5
• Larger numbers: 10, 100
• Invalid inputs: -1, 2.5, "5", null, undefined, [], {}