CREATE TABLE table_25548213_1 (series__number INT, us_viewers__million_ VARCHAR)

What is the series number that had 5.31 million viewers?
SELECT MAX(series__number) FROM table_25548213_1 WHERE us_viewers__million_ = "5.31"
SELECT MAX("series__number") FROM "table_25548213_1" WHERE "5.31" = "us_viewers__million_"