#  Generate a vector of prime numbers that are less than or equal to the
#  scalar argument.  The argument is rounded to an integer, if necessary.
#  If the argument is less than 2, a zero length vector is returned.

primes = function (n)
{
  local (v; i);

  n = integer (scalar (n));
  v = seq (n);

  for (i in seq (floor (sqrt (n)) - 1) + 1)
  {
    if (v[i]) { v[i^2:n:i] = 0; }
  }

  return pick (v > 1);
};

# Compute the prime factors of a positive integer.

primef = function (n)
{
  local (v; r);

  n = integer (scalar (n));
  r = fill (0; 1);

  v = primes (floor (sqrt (n)));

  while (n > 1)
  {
    v = v [pick (!(n%v))];
    if (!v.ne) { v = n; }
    r = r, v;
    n = n / product (v);
  }

  return sort (r);
};