diff --git a/PerfectNumbers.Core/MersenneDivisorCycles.cs b/PerfectNumbers.Core/MersenneDivisorCycles.cs
index 78c60e0..c8d86ee 100644
--- a/PerfectNumbers.Core/MersenneDivisorCycles.cs
+++ b/PerfectNumbers.Core/MersenneDivisorCycles.cs
@@ -398,7 +398,8 @@ public class MersenneDivisorCycles
 		// Atomic.Add(ref _tryFactorIntoCountsInternalHits, 1UL);
 		// Console.WriteLine($"MersenneDivisorCycles.TryFactorIntoCountsInternal hits {Volatile.Read(ref _tryFactorIntoCountsInternalHits)}");
 
-		if (PrimeTester.IsPrimeCpu(remaining, CancellationToken.None))
+		if (PrimeTester.IsPrimeGpu(remaining))
+		// if (PrimeTester.IsPrimeCpu(remaining, CancellationToken.None))
 		{
 			AddFactor(counts, remaining);
 			return true;
@@ -937,7 +938,8 @@ public class MersenneDivisorCycles
 		// }
 
         // if (!skipPrimeOrderHeuristic && HeuristicPrimeTester.Exclusive.IsPrimeCpu(divisor, CancellationToken.None))
-        if (!skipPrimeOrderHeuristic && PrimeTester.IsPrimeCpu(divisor, CancellationToken.None))
+        if (!skipPrimeOrderHeuristic && PrimeTester.IsPrimeGpu(divisor))
+        // if (!skipPrimeOrderHeuristic && PrimeTester.IsPrimeCpu(divisor, CancellationToken.None))
         {
             ulong computedOrder = PrimeOrderCalculator.Calculate(
                     divisor,
diff --git a/PerfectNumbers.Core/PrimeOrderCalculator.Cpu.cs b/PerfectNumbers.Core/PrimeOrderCalculator.Cpu.cs
index 9b83a9c..e03ba2f 100644
--- a/PerfectNumbers.Core/PrimeOrderCalculator.Cpu.cs
+++ b/PerfectNumbers.Core/PrimeOrderCalculator.Cpu.cs
@@ -1133,6 +1133,7 @@ internal static partial class PrimeOrderCalculator
 					// Atomic.Add(ref _partialFactorHits, 1UL);
 					// Console.WriteLine($"Partial factor hits {Volatile.Read(ref _partialFactorHits)}");
 
+					// bool isPrime = PrimeTester.IsPrimeCpu(composite, CancellationToken.None);
 					bool isPrime = PrimeTester.IsPrimeGpu(composite);
 					// bool isPrime = Open.Numeric.Primes.Prime.Numbers.IsPrime(composite);
 
@@ -1200,6 +1201,7 @@ internal static partial class PrimeOrderCalculator
 				// Atomic.Add(ref _partialFactorPendingHits, 1UL);
 				// Console.WriteLine($"Partial factor pending hits {Volatile.Read(ref _partialFactorPendingHits)}");
 
+				// bool isPrime = PrimeTester.IsPrimeCpu(composite, CancellationToken.None);
 				bool isPrime = PrimeTester.IsPrimeGpu(composite);
 				// bool isPrime = Open.Numeric.Primes.Prime.Numbers.IsPrime(composite);
 
@@ -1238,6 +1240,7 @@ internal static partial class PrimeOrderCalculator
 			// Console.WriteLine($"Partial factor cofactor hits {Volatile.Read(ref _partialFactorCofactorHits)}");
 
 			cofactorIsPrime = PrimeTester.IsPrimeCpu(cofactor, CancellationToken.None);
+			// cofactorIsPrime = PrimeTester.IsPrimeGpu(cofactor);
 			// cofactorIsPrime = Open.Numeric.Primes.Prime.Numbers.IsPrime(cofactor);
 		}
 
@@ -1774,8 +1777,8 @@ internal static partial class PrimeOrderCalculator
 		// PrimeTester primeTester = PrimeTester.Exclusive;
 
 		// bool isPrime = primeTester.HeuristicIsPrimeGpu(value);
-		// bool isPrime = PrimeTester.IsPrimeCpu(value, CancellationToken.None);
 		bool isPrime = PrimeTester.IsPrimeCpu(value, CancellationToken.None);
+		// bool isPrime = PrimeTester.IsPrimeGpu(value);
 		// bool isPrime = Open.Numeric.Primes.Prime.Numbers.IsPrime(value);
 		if (!knownComposite && isPrime)
 		{
@@ -1790,8 +1793,8 @@ internal static partial class PrimeOrderCalculator
 		// Console.WriteLine($"Factor completely after PollardRho hits {Volatile.Read(ref _factorCompletelyPollardRhoHits)}");
 
 		// isPrime = primeTester.HeuristicIsPrimeGpu(factor);
-		// isPrime = PrimeTester.IsPrimeCpu(factor, CancellationToken.None);
 		isPrime = PrimeTester.IsPrimeCpu(factor, CancellationToken.None);
+		// isPrime = PrimeTester.IsPrimeGpu(factor);
 		// isPrime = Open.Numeric.Primes.Prime.Numbers.IsPrime(factor);
 		if (isPrime)
 		{
@@ -1828,6 +1831,7 @@ internal static partial class PrimeOrderCalculator
 			// Console.WriteLine($"Partial factor cofactor hits {Volatile.Read(ref _partialFactorCofactorHits)}");
 
 			isPrime = PrimeTester.IsPrimeCpu(quotient, CancellationToken.None);
+			// isPrime = PrimeTester.IsPrimeGpu(quotient);
 			// isPrime = Open.Numeric.Primes.Prime.Numbers.IsPrime(quotient);
 		}