Update app.py

Fixed formula for Pascal sum. Fixed value's type returned by sum_to_num().

app.py

@@ -55,7 +55,7 @@ def sum_to_num(num:int) -> int:
     """
     if isinstance(num, int):
         if num > 1:
-            return num*(num-1)/2
+            return int(num*(num+1)/2)
         else:
             raise Value("Please insert a value greater than 1.")
     else: