input: def largest_prime_factor(n):
      """ Find the largest prime factor of a given number.
      >>> largest_prime_factor(331)
      331
      >>> largest_prime_factor(13195)
      29
      """
      import math
      factors = []
      for i in range(2, int(math.sqrt(n)) + 1):
          if n % i == 0:
              factors.append(i)
              factors.append(int(n/i))
      prime_factors = []
      for potential_factor in factors:
          is_prime = True
          for j in range(2, int(math.sqrt(potential_factor)) + 1):
              if potential_factor % j == 0 and potential_factor != j:
                  is_prime = False
          if is_prime:
              prime_factors.append(potential_factor)
      if prime_factors:
          return max(prime_factors)
      else:
          return n
output:     import math
      factors = []
      for i in range(2, int(math.sqrt(n)) + 1):
          if n % i == 0:
              factors.append(i)
              factors.append(int(n/i))
      prime_factors = []
      for potential_factor in factors:
          is_prime = True
          for j in range(2, int(math.sqrt(potential_factor)) + 1):
              if potential_factor % j == 0 and potential_factor != j:
                  is_prime = False
          if is_prime:
              prime_factors.append(potential_factor)
      if prime_factors:
          return max(prime_factors)
      else:
          return n