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Surname Youdan (又丹 , 友丹 , Youdan ) , around the world, is a rare family name. The family name Youdan is habitual in Australia, where it is a rare surname, the United Kingdom, and New Zealand, where it is a very rare surname. In absolute terms, it is commonest in China, the United Kingdom, and Australia. More frequently, Youdan is the forename as well as the last name.