user: Question: When 656000 is the amount of viewers and N/A is the cable rank what is the airdate?
Columns: ['Episode no.', 'Airdate', 'Viewers', 'BBC Three weekly ranking', 'Cable rank']
Types: ['real', 'text', 'real', 'text', 'text']
Sample row: [1.0, '12 April 2012', 947000.0, '5', '16']
SQL:

assistant: SELECT "Airdate" FROM "Table" WHERE "Cable rank" = 'N/A' AND "Viewers" = 656000.0;