user: Question: What is the original air date when there were 12.81 million u.s viewers?
Columns: ['Series #', 'Episode title', 'Writer(s)', 'Director', 'U.S. viewers (millions)', 'Original air date']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, '" Pilot "', 'Silvio Horta', 'Richard Shepard', '16.32', 'September28,2006']
SQL:

assistant: SELECT "Original air date" FROM "Table" WHERE "U.S. viewers (millions)" = '12.81';