function displayPrimes(current, max) {
                if (current > max)
                    return;

                if (current >= 2) {

                    var valid = true;

                    for (var i = 2; i < current; i++) {
                        if (current % i === 0)
                            valid = false;
                    }

                    if (valid)
                        console.log(current);

                }

                current++;
                displayPrimes(current, max);
            }

            displayPrimes(0, 20);