diff --git a/src/main/java/me/hatter/math/util/MathUtil.java b/src/main/java/me/hatter/math/util/MathUtil.java
index 03c664c..e7ad159 100644
--- a/src/main/java/me/hatter/math/util/MathUtil.java
+++ b/src/main/java/me/hatter/math/util/MathUtil.java
@@ -28,6 +28,7 @@ public class MathUtil {
     public static final BigDecimal LITTLE_NUMBER = new BigDecimal(
             "0.000000000000000000000000000000000000000001");
 
+    // n!, n的阶乘
     public static BigInteger factorial(long n) {
         if (n < 0) {
             throw new RuntimeException("Not supported n < 0");