input: Write a python function to return a list of divisors of a given number.
  assert divisors(15) == [1, 3, 5, 15]
  assert divisors(10) == [1, 2, 5, 10]
  assert divisors(7) == [1, 7]
output: def divisors(n):
      return [i for i in range(1, n + 1) if n % i == 0]