input: Write a function to generate a list of Fibonacci numbers up to a given number.
  assert fibonacci_sequence(10) == [0, 1, 1, 2, 3, 5, 8]
  assert fibonacci_sequence(1) == [0, 1]
  assert fibonacci_sequence(21) == [0, 1, 1, 2, 3, 5, 8, 13]
output: def fibonacci_sequence(n):
      if n < 0:
          return []
      sequence = [0, 1]
      while True:
          next_value = sequence[-1] + sequence[-2]
          if next_value > n:
              break
          sequence.append(next_value)
      return sequence