Performance improvements

PerfectNumbers.Core/ULongExtensions.cs

@@ -168,9 +168,10 @@ public static class ULongExtensions
 
         ulong w1 = xLow * yHigh;
         ulong w2 = xHigh * yLow;
+        ulong w3 = xLow * yLow;
 
         ulong result = (xHigh * yHigh) + (w1 >> 32) + (w2 >> 32);
-                result += (((xLow * yLow) >> 32) + (uint)w1 + (uint)w2) >> 32;
+        result += ((w3 >> 32) + (uint)w1 + (uint)w2) >> 32;
         return result;
     }