Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_21550897_1 (production_code INTEGER, us_viewers__million_ VARCHAR)

### Question ###
What is the production code for the episode that had 9.18 million viewers (U.S.)?

### Accurate SQL ###

SELECT MAX(production_code) FROM table_21550897_1 WHERE us_viewers__million_ = "9.18"