input: Write a python function to generate a list of powers of 3 from 3^0 up to 3^5.
  assert generate_powers_of_3() == [1, 3, 9, 27, 81, 243]
  assert generate_powers_of_3() == [1, 3, 9, 27, 81, 243]
output: def generate_powers_of_3():
      return [3**i for i in range(6)]