f(x) (Korean: 에프엑스) is a five member South Korean girl group formed by SM Entertainment in 2009. The name is a play on the mathematical notation for function, with "f" signifying "flower" and "x" representing the female's double X chromosome. The group made their debut on September 1, 2009 with release of a digital single 라차타 (LA chA TA). The quintet consists of 빅토리아 (Victoria), 엠버 (Amber), 루나 (Luna), 설리 (Sulli) and 크리스탈 (Krystal). Read more about f(x) on Last.fm.