user: Question: What is the production code for the episode with 8.56 million U.S. viewers?
Columns: ['Series #', 'Season #', 'Title', 'Directed by', 'Written by', 'Original air date', 'Production code', 'U.S. viewers (millions)']
Types: ['real', 'real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [169.0, 1.0, '"Day 8: 4:00 p.m.– 5:00 p.m."', 'Brad Turner', 'Howard Gordon & Evan Katz', 'January17,2010', '8AFF01', '11.50']
SQL:

assistant: SELECT "Production code" FROM "Table" WHERE "U.S. viewers (millions)" = '8.56';