CREATE TABLE table_74249 ("\\u2116" FLOAT, "#" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Production code" TEXT, "U.S. viewers  ( millions ) " TEXT)

What is the series No when the season 4 # is 18?
SELECT MIN("\u2116") FROM table_74249 WHERE "#" = '18'
SELECT MIN("\u2116") FROM "table_74249" WHERE "#" = '18'