@article{10_4064_cm92_1_10,
     author = {Florian Luca and Carl Pomerance},
     title = {On some problems of {M/akowski{\textendash}Schinzel} and {Erd\H{o}s
concerning} the arithmetical functions $\phi $ and $\sigma $},
     journal = {Colloquium Mathematicum},
     pages = {111--130},
     publisher = {mathdoc},
     volume = {92},
     number = {1},
     year = {2002},
     doi = {10.4064/cm92-1-10},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/cm92-1-10/}
}