@article{LeavensVermeulen1992,
  author    = {{Gary T. Leavens and Mike Vermeulen}},
  title     = {{$3x +1$ Search Programs}},
  journal   = {{Computers & Mathematics, with Applications}},
  year      = {{1992}},
  volume    = {{24}},
  number    = {{11}},
  pages     = {{79--99}},
  note      = {{MR 93k:68047}},
}