F(x) (group)  f(x) (; ) is a South Korean multinational girl group formed by SM Entertainment. The group's composed of Victoria, Amber, Luna, and Krystal and previously Sulli until her departure from the group in August 2015.  f(x) officially debuted in September 2009 with the release of the digital single "La Cha Ta". Their debut studio album, "Pinocchio" (2011), and their two extended plays "Nu Abo" and "Electric Shock" produced three number one singles on South Korea's Gaon Digital Chart. Their acclaimed second studio album, "Pink Tape" (2013), was the only K-pop album on US music channel Fuse's "41 Best Albums of 2013" and was named "Greatest K-pop Album of the 2010s" by "Billboard". The group's third and fourth albums, "Red Light" (2014) and "4 Walls" (2015), were commercially successful and well-received by music critics. After releasing the SM Station single "All Mine" in 2016, the group halted group promotions and the members have embarked on individual music, acting, and modelling careers. In August 2019, f(x) officially reunited as a three-piece (without Victoria) and performed at the three-night SM Town Live 2019 in Tokyo concert. Known for their experimental style and eclectic, electropop-based sound, f(x) is one of the first few recognized K-pop groups internationally, becoming the first K-pop act to perform at SXSW. In 2017, "Billboard" ranked f(x) at number seven on their "Top 10 K-pop Girl Groups of the Past Decade" list.  f(x) is a function of mathematics, which means that they would carry out various activities, based on the various talents and attractiveness of the members, like the formula whose results change depending on the value of x. In addition, "f" symbolizes flower and "x" symbolizes 'X' on the female chromosome XX which, taken together, symbolizes "flower reminiscent of women." Krystal was scouted by SM Entertainment in 2000 while on a family visit to Korea, along with her sister Jessica (a former member of Girls' Generation). She subsequently appeared in a small role in Shinhwa's music video for the song "Wedding March" ("너의 곁에서 2"). Sulli was a child actress, making her first television appearance in 2005 as the young Princess Seonhwa of Silla in SBS's "Ballad of Seodong".