input: Write a function to perform linear regression for predicting the numbers in a given dataset. Use the provided X and Y values. If the input dataset is empty, return "No data provided".
  assert linear_regression([1,2,3,4,5], [3,5,7,9,13])[0] == 15.0
  assert linear_regression([], []) == "No data provided"
output: def linear_regression(X, Y):
      if not X or not Y:
          return "No data provided"
      
      n = len(X)
      sum_X = sum(X)
      sum_Y = sum(Y)
      sum_XY = sum(x * y for x, y in zip(X, Y))
      sum_X_squared = sum(x ** 2 for x in X)
      
      m = (n * sum_XY - sum_X * sum_Y) / (n * sum_X_squared - sum_X ** 2)
      b = (sum_Y - m * sum_X) / n
      
      return m, b