input: Write a function to print the first n fibonacci numbers.
  assert fibonacci(5) == "0 1 1 2 3"
  assert fibonacci(10) == "0 1 1 2 3 5 8 13 21 34"
  assert fibonacci(1) == "0"
  assert fibonacci(2) == "0 1"
output: def fibonacci(n):
      if n == 1:
          return "0"
      elif n == 2:
          return "0 1"
      
      fib_sequence = [0, 1]
      while len(fib_sequence) < n:
          fib_sequence.append(fib_sequence[-1] + fib_sequence[-2])
      
      return ' '.join(map(str, fib_sequence))