CREATE TABLE table_2645 ("Series #" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Production code" FLOAT)

How many series numbers belong to the episode 'Vexation of Spirit'?
SELECT COUNT("Series #") FROM table_2645 WHERE "Title" = 'Vexation of Spirit'
SELECT COUNT("Series #") FROM "table_2645" WHERE "Title" = 'Vexation of Spirit'