Ô Ăn Quan → Vietnamese. Ô Ăn Quan (literally: "Mandarin Square Capturing"), also known as Ô Láng ("Village Squares"), is a mancala game played by Vietnamese girls usually seven to ten years old. According to Ngô Quý Sơn, the oldest western source on the game, it was once played by boys too. The game is valuable for promoting calculating abilities. It is said that the Vietnamese mathematician Mạc Hiển Tích discovered số ẩn (negative numbers; literally: "hidden / secret number") in 1086 by playing Ô Ăn Quan. Ô Ăn Quan was implemented for mobile phones in Vietnam in 2004.