What is the production code for the episode with 8.56 million U.S. viewers?
CREATE TABLE table_22181917_2 (
    production_code VARCHAR,
    us_viewers__millions_ VARCHAR
)
SELECT production_code FROM table_22181917_2 WHERE us_viewers__millions_ = "8.56"
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: What is the production code for the episode with 8.56 million U.S. viewers? ### Input: CREATE TABLE table_22181917_2 (
    production_code VARCHAR,
    us_viewers__millions_ VARCHAR
) ### Response: SELECT production_code FROM table_22181917_2 WHERE us_viewers__millions_ = "8.56"