from typing import List


def prime_factors(N: int) -> List[int]:
  """
  Compute prime factors of `N`.

  Args:
    An integer.

  Return:
    list[int]: The prime factors of `N`, excluding 1.j
  """
  if N == 1:
    return [1]

  prime_facs = []
  divisor = 2
  while divisor**2 <= N:
    while N % divisor == 0:
      N //= divisor
      prime_facs.append(divisor)
    divisor += 1
  prime_facs.append(N)
  result = [p for p in prime_facs if p > 1]
  return result