FOR HER UPCOMING sixth album, Katy Perry worked with some of the producers who helped craft hits on Teenage Dream and Prism, Rolling Stone has learned. The pop singer reconnected with Max Martin, Dr. Luke, Stargate, and several others for KP6, the informal name for her first album in more than four years. “Katy knew exactly the album she wanted to make and put together the team to make it happen,” a Capitol Records source confirms to Rolling Stone. “And that includes previous collaborators