//! Takes a number `n` and returns all the prime numbers less than `n`
var SieveOfEratosthenes = n => {
    var a = [],
        o = [];
    for (var i = 0; i < n; i++) {a[i] = 1;}

    for (var i = 2; i <= Math.sqrt(n); i++) {
        if (a[i]) {
            for (var j = i * i; j < n; j += i) {
                a[j] = 0;
            }
        }
    }

    for (var i = 2; i < n; i++) {
        if (a[i]) {o.push(i);}
    }

    return o;
}