CREATE TABLE table_26817 ("Episode no." FLOAT, "Airdate" TEXT, "Viewers" FLOAT, "BBC Three weekly ranking" TEXT, "Cable rank" TEXT)

When 656000 is the amount of viewers and n/a is the cable rank what is the airdate?
SELECT "Airdate" FROM table_26817 WHERE "Cable rank" = 'N/A' AND "Viewers" = '656000'
SELECT "Airdate" FROM "table_26817" WHERE "Cable rank" = 'N/A' AND "Viewers" = '656000'