Refine GPU residue prime tables

PerfectNumbers.Core.Tests/PrimesGeneratorTests.cs

@@ -1,4 +1,5 @@
 using FluentAssertions;
+using PerfectNumbers.Core;
 using Xunit;
 
 namespace PerfectNumbers.Core.Tests;
@@ -19,6 +20,45 @@ public class PrimesGeneratorTests
         {
             squares[i].Should().Be(primes[i] * primes[i]);
         }
+
+        primes.Length.Should().Be((int)PerfectNumberConstants.PrimesLimit);
+        squares.Length.Should().Be((int)PerfectNumberConstants.PrimesLimit);
+    }
+
+    [Fact]
+    [Trait("Category", "Fast")]
+    public void Residue_prime_tables_follow_digit_rules()
+    {
+        var lastOne = PrimesGenerator.SmallPrimesLastOne;
+        var lastOnePow2 = PrimesGenerator.SmallPrimesPow2LastOne;
+        var lastSeven = PrimesGenerator.SmallPrimesLastSeven;
+        var lastSevenPow2 = PrimesGenerator.SmallPrimesPow2LastSeven;
+
+        lastOne.Length.Should().Be((int)PerfectNumberConstants.PrimesLimit);
+        lastSeven.Length.Should().Be((int)PerfectNumberConstants.PrimesLimit);
+        lastOnePow2.Length.Should().Be(lastOne.Length);
+        lastSevenPow2.Length.Should().Be(lastSeven.Length);
+
+        lastOne[..5].Should().Equal([3U, 7U, 11U, 13U, 19U]);
+        lastSeven[..5].Should().Equal([3U, 7U, 11U, 13U, 17U]);
+
+        for (int i = 0; i < lastOne.Length; i++)
+        {
+            uint prime = lastOne[i];
+            uint mod10 = prime % 10U;
+            (mod10 == 1U || mod10 == 3U || mod10 == 9U || prime == 7U || prime == 11U)
+                .Should().BeTrue();
+            lastOnePow2[i].Should().Be(prime * (ulong)prime);
+        }
+
+        for (int i = 0; i < lastSeven.Length; i++)
+        {
+            uint prime = lastSeven[i];
+            uint mod10 = prime % 10U;
+            (mod10 == 3U || mod10 == 7U || mod10 == 9U || prime == 11U)
+                .Should().BeTrue();
+            lastSevenPow2[i].Should().Be(prime * (ulong)prime);
+        }
     }
 }