user: Question: Name the production code for number in season being 21
Columns: ['No. in series', 'No. in season', 'Title', 'Directed by', 'Written by', 'Original air date', 'Production code', 'U.S. viewers (millions)']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['101', '1', '" Gossip "', 'Paul Lieberstein', 'Paul Lieberstein', 'September17,2009', '6001', '8.20']
SQL:

assistant: SELECT "Production code" FROM "Table" WHERE "No. in season" = '21';