"Purple Rain-Union" is the sixth episode of the fourth season of the animated comedy series "Bob's Burgers" and the overall 51st episode, the title of the episode is a reference to the song, film, and which sixth studio album by American recording artist Prince, the first to feature his band The Revolution, and is the soundtrack to the 1984 film of the same name?
Purple Rain-Union:  The title of the episode is a reference to the song, film, and album "Purple Rain" by Prince.
i don't know