CREATE TABLE table_3819 ("No. in series" TEXT, "No. in season" TEXT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Production code" TEXT, "U.S. viewers  ( millions ) " TEXT)

When there are 5.2 million u.s. viewers how many numbers in series are there?
SELECT COUNT("No. in series") FROM table_3819 WHERE "U.S. viewers (millions)" = '5.2'
SELECT COUNT("No. in series") FROM "table_3819" WHERE "U.S. viewers (millions)" = '5.2'