CREATE TABLE table_17906 ("Series number" TEXT, "Episode number" FLOAT, "Date of first broadcast" TEXT, "Total viewers" FLOAT, "Series average" FLOAT)

what is the series number where the date of first broadcast is 16 october 2008?
SELECT "Series number" FROM table_17906 WHERE "Date of first broadcast" = '16 October 2008'
SELECT "Series number" FROM "table_17906" WHERE "Date of first broadcast" = '16 October 2008'