@article{Venturini1992,
  author    = {{Giovanni Venturini}},
  title     = {{Iterates of Number Theoretic Functions with Periodic Rational Coefficients (Generalization of the $3x + 1$ problem)}},
  journal   = {{Studies in Applied Math.}},
  year      = {{1992}},
  volume    = {{86}},
  pages     = {{185--218}},
  note      = {{MR 93b:11102}},
}