@article{JRAM_1979__310_152160,
     author = {Anne L. Ludington},
     title = {A bound on {Kaprekar} constants.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {196--203},
     publisher = {mathdoc},
     volume = {310},
     year = {1979},
     zbl = {0409.10005},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1979__310_152160/}
}