input: Write a python function to find and return the divisors of a number.
  assert find_divisors(10) == [1, 2, 5, 10]
  assert find_divisors(15) == [1, 3, 5, 15]
  assert find_divisors(21) == [1, 3, 7, 21]
output: def find_divisors(n):
      return [i for i in range(1, n+1) if n % i == 0]