fix math formula style

billryan · billryan · commit fc137c19cac3 · 2017-04-03T15:38:36.000+08:00
diff --git a/zh-hans/math_and_bit_manipulation/happy_number.md b/zh-hans/math_and_bit_manipulation/happy_number.md
@@ -17,12 +17,12 @@ and repeat the process until the number equals 1 (where it will stay), or it
 loops endlessly in a cycle which does not include 1. Those numbers for which
 this process ends in 1 are happy numbers.
 
-**Example: **19 is a happy number
+**Example: ** 19 is a happy number
 
-  * 12 \+ 92 = 82
-  * 82 \+ 22 = 68
-  * 62 \+ 82 = 100
-  * 12 \+ 02 \+ 02 = 1
+  * $$1^2 + 9^2 = 82$$
+  * $$8^2 + 2^2 = 68$$
+  * $$6^2 + 8^2 = 100$$
+  * $$1^2 + 0^2 + 0^2 = 1$$
 
 **Credits:**  
 Special thanks to [@mithmatt](https://leetcode.com/discuss/user/mithmatt) and
