CREATE TABLE table_29054902_1 (production_code VARCHAR, us_viewers__million_ VARCHAR)

What is the production code of the episode that was watched by 3.81 million U.S. viewers?
SELECT production_code FROM table_29054902_1 WHERE us_viewers__million_ = "3.81"
SELECT "production_code" FROM "table_29054902_1" WHERE "3.81" = "us_viewers__million_"