CREATE TABLE table_1121 ("Series #" FLOAT, "Season #" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Production Code" FLOAT, "U.S. viewers  ( millions ) " TEXT)

How many series had 18.77 million viewers?
SELECT COUNT("Series #") FROM table_1121 WHERE "U.S. viewers (millions)" = '18.77'
SELECT COUNT("Series #") FROM "table_1121" WHERE "U.S. viewers (millions)" = '18.77'