What episode number in the series was viewed by 13.66 million people in the U.S.?
CREATE TABLE table_27978 (
    "No. in series" real,
    "Title" text,
    "Directed by" text,
    "Written by" text,
    "Original air date" text,
    "Production code" text,
    "U.S. viewers (million)" text
)
SELECT MAX("No. in series") FROM table_27978 WHERE "U.S. viewers (million)" = '13.66'
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 episode number in the series was viewed by 13.66 million people in the U.S.? ### Input: CREATE TABLE table_27978 (
    "No. in series" real,
    "Title" text,
    "Directed by" text,
    "Written by" text,
    "Original air date" text,
    "Production code" text,
    "U.S. viewers (million)" text
) ### Response: SELECT MAX("No. in series") FROM table_27978 WHERE "U.S. viewers (million)" = '13.66'