CREATE TABLE table_16879 ("No. in series" TEXT, "No. in season" TEXT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Featured character ( s ) " TEXT, "Original air date" TEXT, "U.S. viewers  ( million ) " TEXT)

What are the episode numbers where the episode features Jack & Locke?
SELECT "No. in series" FROM table_16879 WHERE "Featured character(s)" = 'Jack & Locke'
SELECT "No. in series" FROM "table_16879" WHERE "Featured character(s)" = 'Jack & Locke'