diff --git a/DIRECTORY.md b/DIRECTORY.md
index 78880457..38fcf632 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -245,6 +245,8 @@
     * [Sol1](https://github.com/TheAlgorithms/C/blob/master/project_euler/Problem%2015/sol1.c)
   * Problem 16
     * [Sol1](https://github.com/TheAlgorithms/C/blob/master/project_euler/Problem%2016/sol1.c)
+  * Problem 401
+    * [Sol1](https://github.com/TheAlgorithms/C/blob/master/project_euler/Problem%20401/sol1.c)
 
 ## Searching
   * [Binary Search](https://github.com/TheAlgorithms/C/blob/master/searching/Binary_Search.c)