CREATE TABLE table_2390 ("Episode" FLOAT, "First Air Date" TEXT, "Rating  ( 18\\u201349 ) " TEXT, "Share  ( 18\\u201349 ) " FLOAT, "Viewers  ( millions ) " TEXT, "Rank  ( timeslot ) " TEXT)

Name the rank timeslot for 18-49 share being 13
SELECT COUNT("Rank (timeslot)") FROM table_2390 WHERE "Share (18\u201349)" = '13'
SELECT COUNT("Rank (timeslot)") FROM "table_2390" WHERE "Share (18\u201349)" = '13'