@article{10_4064_cm108_1_4,
     author = {Jean-Marie De Koninck and Florian Luca},
     title = {On the composition of
 the {Euler} function and the sum of divisors function},
     journal = {Colloquium Mathematicum},
     pages = {31--51},
     publisher = {mathdoc},
     volume = {108},
     number = {1},
     year = {2007},
     doi = {10.4064/cm108-1-4},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/cm108-1-4/}
}