@article{Wagon1985,
  author    = {{Stanley Wagon}},
  title     = {{The Collatz problem}},
  journal   = {{Math. Intelligencer}},
  year      = {{1985}},
  volume    = {{7}},
  number    = {{1}},
  pages     = {{72-76}},
  note      = {{MR 86d:11103, Zbl. 566.10008}},
}