Initial commit.

PerfectNumbers.Core/StringBuilderPool.cs

@@ -0,0 +1,17 @@
+using System.Collections.Concurrent;
+using System.Text;
+
+namespace PerfectNumbers.Core;
+
+public static class StringBuilderPool
+{
+    private static readonly ConcurrentQueue<StringBuilder> _stringBuilderPool = new();
+
+    public static StringBuilder Rent() => _stringBuilderPool.TryDequeue(out var sb) ? sb : new();
+
+    public static void Return(StringBuilder sb)
+    {
+        _ = sb.Clear();
+        _stringBuilderPool.Enqueue(sb);
+    }
+}