@article{10_1007_s10587_015_0218_x,
     author = {Sawkmie, Amplify and Singh, Madan Mohan},
     title = {On the tree structure of the power digraphs modulo $n$},
     journal = {Czechoslovak Mathematical Journal},
     pages = {923--945},
     publisher = {mathdoc},
     volume = {65},
     number = {4},
     year = {2015},
     doi = {10.1007/s10587-015-0218-x},
     mrnumber = {3441326},
     zbl = {06537701},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.1007/s10587-015-0218-x/}
}