Added armstrong_number.py program for hactoberfest

Author: Renuka-Kamani

maths/armstrong_number.py

@@ -0,0 +1,23 @@
+def is_armstrong(num: int) -> bool:
+    """
+    Check if a number is an Armstrong number.
+
+    Args:
+        num (int): Number to check
+
+    Returns:
+        bool: True if Armstrong, False otherwise
+    """
+    digits = str(num)
+    power = len(digits)
+    total = sum(int(digit) ** power for digit in digits)
+    return total == num
+
+
+if __name__ == "__main__":  # <-- corrected here
+    # Example usage
+    number = 153
+    if is_armstrong(number):
+        print(f"{number} is an Armstrong number.")
+    else:
+        print(f"{number} is not an Armstrong number.")