@article{HalbeisenHungerbuhler1997,
  author    = {{Lorenz Halbeisen and Norbert Hungerbühler}},
  title     = {{Optimal bounds for the length of rational Collatz cycles}},
  journal   = {{Acta Arithmetica}},
  year      = {{1997}},
  volume    = {{78}},
  pages     = {{227--239}},
  note      = {{MR 98g:11025}},
}