"3" is a song by American singer Britney Spears from her second greatest hits album, The Singles Collection (2009). It was written and produced by Max Martin and Shellback, with additional writing from Tiffany Amber. The song was released on September 29, 2009, by Jive Records, as the only single from The Singles Collection. "3" is an uptempo electropop song that features a heavy bassline and synthesizers, and lyrics that talk about threesomes, while referencing American folk-singing trio Peter, Paul and Mary during the chorus as sexual slang.