input: Write a python function to check if a number is an Armstrong number.
  assert is_armstrong_number(153) == True
  assert is_armstrong_number(9474) == True
  assert is_armstrong_number(123) == False
output: def is_armstrong_number(number):
      digits = [int(d) for d in str(number)]
      power = len(digits)
      return sum(d ** power for d in digits) == number