Add algorithm to check Armstrong number

Author: ARRVINDH PK

maths/is_armstrong_number.py

@@ -0,0 +1,26 @@
+def is_armstrong_number(number: int) -> bool:
+    """
+    Check if a number is an Armstrong number.
+    An Armstrong number is a number that is equal to the sum
+    of its own digits each raised to the power of the number of digits.
+
+    >>> is_armstrong_number(153)
+    True
+    >>> is_armstrong_number(370)
+    True
+    >>> is_armstrong_number(371)
+    True
+    >>> is_armstrong_number(9474)
+    True
+    >>> is_armstrong_number(123)
+    False
+    """
+    digits = str(number)
+    power = len(digits)
+    return number == sum(int(digit) ** power for digit in digits)
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()