CREATE TABLE table_3020 ("Overall" FLOAT, "No. in series" FLOAT, "Title" TEXT, "Directed by" TEXT, "Original air date" TEXT, "U.S. viewers  ( in millions ) " TEXT)

What episode number in the series had 2.528 million u.s. viewers?
SELECT "No. in series" FROM table_3020 WHERE "U.S. viewers (in millions)" = '2.528'
SELECT "No. in series" FROM "table_3020" WHERE "U.S. viewers (in millions)" = '2.528'