@article{Clark1995,
  author    = {{Dean Clark}},
  title     = {{Second-Order Difference Equations Related to the Collatz $3n+1$ Conjecture}},
  journal   = {{J. Difference Equations & Appl.}},
  year      = {{1995}},
  volume    = {{1}},
  pages     = {{73--85}},
  note      = {{MR 96e:11031}},
}