old_contents: def prime_factors(n):
      factors = []
      factor = 2
      while n != 1:
          while n % factor == 0:
              factors += [factor]
              n //= factor
          factor += 1
      return factors
  
new_contents: def prime_factors(n):
      factors = []
      while n % 2 == 0:
          factors += [2]
          n //= 2
      factor = 3
      while n != 1:
          while n % factor == 0:
              factors += [factor]
              n //= factor
          factor += 2
      return factors
  
subject: Make solution more efficient by only testing odd numbers