JSFiddle - React, Tailwind, and code Playground

by infous

JavaScript

/**
 * https://en.wikipedia.org/wiki/Triangular_number
 * Sum of first N natural numbers.
 */
function tn(n) {
    var res = 0;
    
    // 1. Tn = 1 + 2 + 3 + ... + (n - 2) + (n -1) + n;
    for (var i = 1; i <= n; i++) {
        res += i;
    }
    
    // 2. Tn = 1/2 * n * (n + 1)
    //res = n / 2 * (n + 1); // 10 / 2 * 11
    
    // 3. Tn = (n + 1) / 2 - Binomial_coefficient
    //var k = (n + 1) / 2;
    //res = n * k;
    
    alert(res);
}

tn(10);