@article{Levy2004,
  author    = {{Dan Levy}},
  title     = {{Injectivity and Surjectivity of Collatz Functions}},
  journal   = {{Discrete Math.}},
  year      = {{2004}},
  volume    = {{285}},
  pages     = {{190--199}},
  note      = {{MR 2005f:11036}},
}