updating DIRECTORY.md

Author: github-actions

DIRECTORY.md

@@ -42,7 +42,8 @@
     * [Absmin](https://github.com/TheAlgorithms/F-Sharp/blob/main/Algorithms/Math/AbsMin.fs)
     * [Factorial](https://github.com/TheAlgorithms/F-Sharp/blob/main/Algorithms/Math/Factorial.fs)
     * [Fibonacci](https://github.com/TheAlgorithms/F-Sharp/blob/main/Algorithms/Math/Fibonacci.fs)
-    * [Perfectnumbers](https://github.com/TheAlgorithms/F-Sharp/blob/main/Algorithms/Math/PerfectNumbers.fs)
+    * [Greatest Common Divisor](https://github.com/TheAlgorithms/F-Sharp/blob/main/Algorithms/Math/Greatest_Common_Divisor.fs)
+    * [Perfect Numbers](https://github.com/TheAlgorithms/F-Sharp/blob/main/Algorithms/Math/Perfect_Numbers.fs)
     * [Power](https://github.com/TheAlgorithms/F-Sharp/blob/main/Algorithms/Math/Power.fs)
     * [Prime](https://github.com/TheAlgorithms/F-Sharp/blob/main/Algorithms/Math/Prime.fs)
   * Search