How many times is the formula tl 2 ba 2 cuo 6?
CREATE TABLE table_15971 (
    "Formula" text,
    "Notation" text,
    "T c (K)" real,
    "No. of Cu-O planes in unit cell" real,
    "Crystal structure" text
)
SELECT "No. of Cu-O planes in unit cell" FROM table_15971 WHERE "Formula" = 'Tl 2 Ba 2 CuO 6'
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: How many times is the formula tl 2 ba 2 cuo 6? ### Input: CREATE TABLE table_15971 (
    "Formula" text,
    "Notation" text,
    "T c (K)" real,
    "No. of Cu-O planes in unit cell" real,
    "Crystal structure" text
) ### Response: SELECT "No. of Cu-O planes in unit cell" FROM table_15971 WHERE "Formula" = 'Tl 2 Ba 2 CuO 6'