prime-factors.js

prime-factors.js

var getPrimeFactors = function (number) {
    var i = 2;
    var limit = Math.floor(number/2);
    var factors = [];
    while (i < limit) {
        // Check if number is divisible by i, if yes add i to list of factors and repeat
        // (There can be multiple prime factors of the same value, e.g. 12=2*2*3)
        while (number % i === 0) {
            number /= i;
            factors.push(i);
            console.log("Added factor i = "+i+"; new number to test = "+number);
        }
        i++;
        // Lower the limit so the loop does only run as long as necessary
        limit = Math.floor(number/2);
    }
    // After going through all the lower numbers, the remaining on must be (?) prime
    factors.push(number);
    console.log("Added factor number = "+number+"; program finished");
    return factors;
}
var number = 600851475143;
var array = getPrimeFactors(number);
console.log("Prime factors of "+number+" are "+array);
// should be 71, 839, 1471, 6857 (Wolfram Alpha)