diff --git a/AdventOfCode.lpi b/AdventOfCode.lpi
index ac855eb..eb33314 100644
--- a/AdventOfCode.lpi
+++ b/AdventOfCode.lpi
@@ -65,6 +65,10 @@
         <Filename Value="solvers\UHauntedWasteland.pas"/>
         <IsPartOfProject Value="True"/>
       </Unit>
+      <Unit>
+        <Filename Value="UNumberTheory.pas"/>
+        <IsPartOfProject Value="True"/>
+      </Unit>
     </Units>
   </ProjectOptions>
   <CompilerOptions>
diff --git a/AdventOfCode.lpr b/AdventOfCode.lpr
index 4d5448f..5139121 100644
--- a/AdventOfCode.lpr
+++ b/AdventOfCode.lpr
@@ -26,7 +26,7 @@ uses
   Classes, SysUtils, CustApp,
   USolver,
   UTrebuchet, UCubeConundrum, UGearRatios, UScratchcards, UGiveSeedFertilizer, UWaitForIt, UCamelCards,
-  UHauntedWasteland;
+  UHauntedWasteland, UNumberTheory;
 
 type
 
diff --git a/UNumberTheory.pas b/UNumberTheory.pas
new file mode 100644
index 0000000..f46ce3e
--- /dev/null
+++ b/UNumberTheory.pas
@@ -0,0 +1,60 @@
+{
+  Solutions to the Advent Of Code.
+  Copyright (C) 2023  Stefan Müller
+
+  This program is free software: you can redistribute it and/or modify it under
+  the terms of the GNU General Public License as published by the Free Software
+  Foundation, either version 3 of the License, or (at your option) any later
+  version.
+
+  This program is distributed in the hope that it will be useful, but WITHOUT
+  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+  FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License along with
+  this program.  If not, see <http://www.gnu.org/licenses/>.
+}
+
+unit UNumberTheory;
+
+{$mode ObjFPC}{$H+}
+
+interface
+
+uses
+  Classes, SysUtils;
+
+type
+
+  { TNumberTheory }
+
+  TNumberTheory = class
+  public
+    class function GreatestCommonDivisor(AValue1, AValue2: Integer): Integer;
+    class function LeastCommonMultiple(AValue1, AValue2: Integer): Integer;
+  end;
+
+implementation
+
+{ TNumberTheory }
+
+class function TNumberTheory.GreatestCommonDivisor(AValue1, AValue2: Integer): Integer;
+var
+  t: Integer;
+begin
+  while AValue2 <> 0 do
+  begin
+    t := AValue2;
+    AValue2 := AValue1 mod AValue2;
+    AValue1 := t;
+  end;
+  Result := AValue1;
+end;
+
+class function TNumberTheory.LeastCommonMultiple(AValue1, AValue2: Integer): Integer;
+begin
+  Result := (Abs(AValue1) div GreatestCommonDivisor(AValue1, AValue2)) * Abs(AValue2);
+end;
+
+end.
+