Returning the nth even number using JavaScript

We are required to write a JavaScript function that takes in a number n and returns the nth even number in the sequence of natural numbers.

Problem

Given a positive integer n, find the nth even number. For example, the 1st even number is 2, the 2nd even number is 4, the 3rd even number is 6, and so on.

Understanding the Pattern

Even numbers follow a simple pattern: 2, 4, 6, 8, 10, 12... The nth even number can be calculated using the formula: n × 2.

Example Implementation

Here's how to implement this solution:

const num = 67765;

const nthEven = (n = 1) => {
    return n * 2;
};

console.log(`The ${num}th even number is: ${nthEven(num)}`);

The 67765th even number is: 135530

Step-by-Step Examples

Let's verify with smaller numbers to understand the pattern:

const nthEven = (n) => n * 2;

// Test with first few even numbers
console.log("1st even number:", nthEven(1));   // 2
console.log("2nd even number:", nthEven(2));   // 4
console.log("3rd even number:", nthEven(3));   // 6
console.log("5th even number:", nthEven(5));   // 10
console.log("10th even number:", nthEven(10)); // 20

1st even number: 2
2nd even number: 4
3rd even number: 6
5th even number: 10
10th even number: 20

Alternative Approach with Validation

Here's a more robust version with input validation:

const findNthEven = (n) => {
    if (n <= 0 || !Number.isInteger(n)) {
        return "Please provide a positive integer";
    }
    return n * 2;
};

console.log(findNthEven(100));    // 200
console.log(findNthEven(-5));     // Please provide a positive integer
console.log(findNthEven(0));      // Please provide a positive integer
console.log(findNthEven(1.5));    // Please provide a positive integer

200
Please provide a positive integer
Please provide a positive integer
Please provide a positive integer

Conclusion

Finding the nth even number is straightforward using the formula n × 2. This mathematical approach is more efficient than iterating through numbers to count even ones.