CREATE TABLE table_25668 ("No. in series" FLOAT, "No. in season" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Prod. code" TEXT, "Viewers  ( millions ) " TEXT)

Name the production code for 4.92 million viewers
SELECT "Prod. code" FROM table_25668 WHERE "Viewers (millions)" = '4.92'
SELECT "Prod. code" FROM "table_25668" WHERE "Viewers (millions)" = '4.92'