CREATE TABLE table_21624 ("Series #" FLOAT, "Season #" FLOAT, "Title" CLOB, "Directed by" CLOB, "Written by" CLOB, "Original air date" CLOB)

For series number 256, what was the original air date?
SELECT "Original air date" FROM table_21624 WHERE "Series #" = '256'
SELECT "Original air date" FROM "table_21624" WHERE "Series #" = '256'