human
Considering the provided database schema and associated query, produce SQL code to retrieve the answer to the query. 
###Database Schema: No., #, Title, Directed by, Written by, U.S. viewers (million), Original air date, Production code
###Question: What is the production code for the episode that had 9.18 million viewers (U.S.)?
gpt
SELECT MAX Production code FROM table WHERE U.S. viewers (million) = 9.18