diff --git a/README.md b/README.md
index c9e45d93..74c19d7a 100644
--- a/README.md
+++ b/README.md
@@ -8,7 +8,6 @@
 [![Build status](https://ci.appveyor.com/api/projects/status/sb279kxuv1be391g?svg=true)](https://ci.appveyor.com/project/AtsushiSakai/pythonrobotics)
 [![codecov](https://codecov.io/gh/AtsushiSakai/PythonRobotics/branch/master/graph/badge.svg)](https://codecov.io/gh/AtsushiSakai/PythonRobotics)
 [![Language grade: Python](https://img.shields.io/lgtm/grade/python/g/AtsushiSakai/PythonRobotics.svg?logo=lgtm&logoWidth=18)](https://lgtm.com/projects/g/AtsushiSakai/PythonRobotics/context:python)
-[![CodeFactor](https://www.codefactor.io/repository/github/atsushisakai/pythonrobotics/badge/master)](https://www.codefactor.io/repository/github/atsushisakai/pythonrobotics/overview/master)
 [![tokei](https://tokei.rs/b1/github/AtsushiSakai/PythonRobotics)](https://github.com/AtsushiSakai/PythonRobotics)
 
 Python codes for robotics algorithm.
diff --git a/requirements.txt b/requirements.txt
index 77a0bea4..7c60c4a2 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,3 +3,4 @@ scipy == 1.7.2
 pandas == 1.3.4
 matplotlib == 3.4.3
 cvxpy == 1.1.17
+IPython == 7.29.0 # For sphinx documentation