primeFactors.js

/* (**) Determine the prime factors of a given positive integer.
 *      Construct a flat list containing the prime factors in ascending order.
 *      Example:
 *      * (prime-factors 315)
 *      (3 3 5 7)
 */

function prime(n) {
  if (n < 2) {
    return false;
  } else if (n == 2) {
    return true;
  } else if (n % 2 == 0) {
    return false;
  }
  
  var i = 3;

  while(i < n) {
    if (n % i == 0)
      return false;

    i += 2;
  }

  return true
}

function primeFactors(n) {
  var numbers = []
    , i = 2;

  while (i < n) {
    if (n % i == 0 && prime(i))
      numbers.push(i);

    if (i == 2) {
      i++;
    } else {
      i += 2;
    }
  }

  return numbers;
}