user: Question: What was the airdate of 21 series number?
Columns: ['Series no.', 'Title', 'Directed by', 'Written by', 'Original air date', 'Production Code']
Types: ['real', 'text', 'text', 'text', 'text', 'real']
Sample row: [1.0, '"Bully and the Beast"', 'Tyler Perry', 'Kellie R. Griffin', 'June6,2007', 101.0]
SQL:

assistant: SELECT "Original air date" FROM "Table" WHERE "Series no." = 21.0;