@article{HoffmanKlarner1978,
  author    = {{Dean G. Hoffman and David A. Klarner}},
  title     = {{Sets of integers closed under affine operators- the closure of finite sets}},
  journal   = {{Pacific Journal of Mathematics}},
  year      = {{1978}},
  volume    = {{78}},
  number    = {{2}},
  pages     = {{337--344}},
  note      = {{MR 80i:10075}},
}