diff --git a/math/computational_geometry/notes.page b/math/computational_geometry/notes.page
index b952b7f..1c6d3ab 100644
--- a/math/computational_geometry/notes.page
+++ b/math/computational_geometry/notes.page
@@ -90,5 +90,5 @@ $P$ if and only if $P$ is a convex polygon.
 
 **Theorem 1.19**
 : The number of triangulations of a convex polygon with $n + 2$
-vertices is the Catalan number $$ C_n = \frac{1}{n + 1}{n + 1 \choose
-n} $$
+vertices is the Catalan number $$ C_n = \frac{1}{n + 1}{2n \choose n}
+$$