Adding Armstrong number (#1708)

* Adding Armstrong number

* Update armstrong_numbers

* Update armstrong_numbers.py

* Update armstrong_numbers.py

* Update armstrong_numbers.py

Co-authored-by: Christian Clauss <cclauss@me.com>

maths/armstrong_numbers.py

@@ -0,0 +1,55 @@
+"""
+An Armstrong number is a number that is equal to the sum of the cubes of its digits.
+For example, 370 is an Armstrong number because 3*3*3 + 7*7*7 + 0*0*0 = 370.
+An Armstrong number is often called Narcissistic number.
+"""
+
+
+def armstrong_number(n: int) -> bool:
+    """
+    This function checks if a number is Armstrong or not.
+
+    >>> armstrong_number(153)
+    True
+    >>> armstrong_number(200)
+    False
+    >>> armstrong_number(1634)
+    True
+    >>> armstrong_number(0)
+    False
+    >>> armstrong_number(-1)
+    False
+    >>> armstrong_number(1.2)
+    False
+    """
+    if not isinstance(n, int) or n < 1:
+        return False
+    
+    # Initialization of sum and number of digits.
+    sum = 0
+    number_of_digits = 0
+    temp = n
+    # Calculation of digits of the number
+    while temp > 0:
+        number_of_digits += 1
+        temp //= 10
+    # Dividing number into separate digits and find Armstrong number
+    temp = n
+    while temp > 0:
+        rem = temp % 10
+        sum += (rem ** number_of_digits)
+        temp //= 10
+    return n == sum
+
+
+# In main function user inputs a number to find out if it's an Armstrong or not. Th function armstrong_number is called.
+def main():
+    num = int(input("Enter an integer number to check if it is Armstrong or not: ").strip())
+    print(f"{num} is {'' if armstrong_number(num) else 'not '}an Armstrong number.")
+
+
+if __name__ == '__main__':
+    import doctest
+
+    doctest.testmod()
+    main()