diff --git a/DIRECTORY.md b/DIRECTORY.md
index 7db9ca18..ec130f6b 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -266,6 +266,8 @@
     * [Sol1](https://github.com/kvedala/C/blob/master/project_euler/Problem%2025/sol1.c)
   * Problem 26
     * [Sol1](https://github.com/kvedala/C/blob/master/project_euler/Problem%2026/sol1.c)
+  * Problem 401
+    * [Sol1](https://github.com/kvedala/C/blob/master/project_euler/Problem%20401/sol1.c)
 
 ## Searching
   * [Binary Search](https://github.com/kvedala/C/blob/master/searching/Binary_Search.c)