input: Write a python function to find outliers in a numpy array based on 3 standard deviations from the mean.
  assert find_outliers(np.array([2, 3, 1, 4, 5, 6, 5, 8, 9, 10, 11, 12])) == [1, 11, 12]
  assert find_outliers(np.array([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 100])) == [100]
  assert find_outliers(np.array([10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30])) == []
output: import numpy as np
  
  def find_outliers(arr):
      mean = np.mean(arr)
      std_dev = np.std(arr)
      outliers = [x for x in arr if abs(x - mean) > 3 * std_dev]
      return outliers