Allow exhaustive divisor scans with 128-bit limits

PerfectNumbers.Core/PerfectNumberConstants.cs

@@ -5,6 +5,6 @@ public static class PerfectNumberConstants
 	public const ulong BiggestKnownEvenPerfectP = 136279841UL;
 	public static readonly uint PrimesLimit = 1_000_000; //(ulong)Array.MaxLength;// 1_000_000;
 	public const int MaxQForDivisorCycles = 4_000_000;
-	public const int ExtraDivisorCycleSearchLimit = 64;
+        public const ulong ExtraDivisorCycleSearchLimit = 64UL;
 
-}
+}