f(x) is a South Korean girl group formed by SM Entertainment in 2009. The name is a play on the mathematical notation for function. The group members have also been nicknamed "function girls". The group made their debut on September 5, 2009 with release of a digital single "La Cha Ta" (stylized as "LA chA TA"). The quintet consists of Victoria, Amber, Luna, Sulli, and Krystal.