diff --git a/PerfectNumbers.Core.Tests/HeuristicCombinedPrimeTesterTests.cs b/PerfectNumbers.Core.Tests/HeuristicCombinedPrimeTesterTests.cs
index a03ccc5..307fdc7 100644
--- a/PerfectNumbers.Core.Tests/HeuristicCombinedPrimeTesterTests.cs
+++ b/PerfectNumbers.Core.Tests/HeuristicCombinedPrimeTesterTests.cs
@@ -13,7 +13,7 @@ public class HeuristicCombinedPrimeTesterTests
     [InlineData((byte)1)]
     [InlineData((byte)7)]
     [InlineData((byte)9)]
-    public void Enumerator_uses_two_a_one_b_schedule_by_default(byte lastDigit)
+    public void Enumerator_uses_one_a_one_b_schedule_by_default(byte lastDigit)
     {
         Span<HeuristicCombinedPrimeTester.HeuristicGroupBSequenceState> groupBState =
             stackalloc HeuristicCombinedPrimeTester.HeuristicGroupBSequenceState[4];
@@ -26,7 +26,8 @@ public class HeuristicCombinedPrimeTesterTests
             results.Add(candidate);
         }
 
-        results.Count.Should().BeGreaterThanOrEqualTo(16);
+        const int segmentsToCheck = 6;
+        results.Count.Should().BeGreaterThanOrEqualTo(4 + segmentsToCheck * 2);
         results[0].Value.Should().Be(3UL);
         results[0].Group.Should().Be(HeuristicCombinedPrimeTester.HeuristicDivisorGroup.GroupAConstant);
         results[1].Value.Should().Be(7UL);
@@ -37,25 +38,51 @@ public class HeuristicCombinedPrimeTesterTests
         results[3].Group.Should().Be(HeuristicCombinedPrimeTester.HeuristicDivisorGroup.GroupAConstant);
 
         int index = 4;
-        const int segmentsToCheck = 3;
 
         for (int segment = 0; segment < segmentsToCheck; segment++)
         {
-            for (int i = 0; i < 2; i++)
-            {
-                HeuristicCombinedPrimeTester.HeuristicDivisorCandidate groupACandidate = results[index++];
-                groupACandidate.Value.Should().BeGreaterThan(13UL);
-                (groupACandidate.Value % 10UL).Should().Be(3UL);
-                groupACandidate.Group.Should().NotBe(HeuristicCombinedPrimeTester.HeuristicDivisorGroup.GroupB);
-            }
+            HeuristicCombinedPrimeTester.HeuristicDivisorCandidate groupACandidate = results[index++];
+            groupACandidate.Value.Should().BeGreaterThan(13UL);
+            (groupACandidate.Value % 10UL).Should().Be(3UL);
+            groupACandidate.Group.Should().NotBe(HeuristicCombinedPrimeTester.HeuristicDivisorGroup.GroupB);
 
-            for (int i = 0; i < 1; i++)
-            {
-                HeuristicCombinedPrimeTester.HeuristicDivisorCandidate groupBCandidate = results[index++];
-                groupBCandidate.Value.Should().BeGreaterThan(13UL);
-                (groupBCandidate.Value % 10UL).Should().NotBe(3UL);
-                groupBCandidate.Group.Should().Be(HeuristicCombinedPrimeTester.HeuristicDivisorGroup.GroupB);
-            }
+            HeuristicCombinedPrimeTester.HeuristicDivisorCandidate groupBCandidate = results[index++];
+            groupBCandidate.Value.Should().BeGreaterThan(13UL);
+            (groupBCandidate.Value % 10UL).Should().NotBe(3UL);
+            groupBCandidate.Group.Should().Be(HeuristicCombinedPrimeTester.HeuristicDivisorGroup.GroupB);
+        }
+
+    }
+
+    [Theory]
+    [Trait("Category", "Fast")]
+    [InlineData((byte)1)]
+    [InlineData((byte)7)]
+    [InlineData((byte)9)]
+    public void One_a_one_b_pattern_interleaves_group_a_and_group_b_values(byte lastDigit)
+    {
+        ReadOnlySpan<uint> combined = HeuristicCombinedPrimeTester.GetCombinedDivisors(
+            lastDigit,
+            HeuristicCombinedPrimeTester.CombinedDivisorPattern.OneAOneB);
+
+        combined.Length.Should().BeGreaterThan(18);
+        combined[0].Should().Be(3U);
+        combined[1].Should().Be(7U);
+        combined[2].Should().Be(11U);
+        combined[3].Should().Be(13U);
+
+        int index = 4;
+        const int segmentsToCheck = 6;
+
+        for (int segment = 0; segment < segmentsToCheck; segment++)
+        {
+            uint groupAValue = combined[index++];
+            groupAValue.Should().BeGreaterThan(13U);
+            (groupAValue % 10U).Should().Be(3U);
+
+            uint groupBValue = combined[index++];
+            groupBValue.Should().BeGreaterThan(13U);
+            (groupBValue % 10U).Should().NotBe(3U);
         }
     }
 
diff --git a/PerfectNumbers.Core/HeuristicCombinedPrimeTester.cs b/PerfectNumbers.Core/HeuristicCombinedPrimeTester.cs
index 240180f..88d36c5 100644
--- a/PerfectNumbers.Core/HeuristicCombinedPrimeTester.cs
+++ b/PerfectNumbers.Core/HeuristicCombinedPrimeTester.cs
@@ -428,7 +428,7 @@ Cleanup:
 
     private static ReadOnlySpan<uint> GetCombinedDivisors(byte nMod10)
     {
-        return GetCombinedDivisors(nMod10, CombinedDivisorPattern.TwoAOneB);
+        return GetCombinedDivisors(nMod10, CombinedDivisorPattern.OneAOneB);
     }
 
     internal static ReadOnlySpan<uint> GetCombinedDivisors(byte nMod10, CombinedDivisorPattern pattern)