input: 
  from typing import List
  
  def is_armstrong_number(num: int) -> bool:
      """ Check if a given number is an Armstrong number.
      An Armstrong number of n digits is a number that equals the sum of its digits each raised to the nth power.
      >>> is_armstrong_number(153)
      True
      >>> is_armstrong_number(9474)
      True
      >>> is_armstrong_number(123)
      False
      """
  
output:     digits = [int(d) for d in str(num)]
      n = len(digits)
      return num == sum(d ** n for d in digits)