@article{10_4064_aa138_4_4,
     author = {Mohand-Ouamar Hernane and Florian Luca},
     title = {On the independence of $\sigma (\phi (n))$ and $\phi (\sigma (n))$},
     journal = {Acta Arithmetica},
     pages = {337--346},
     publisher = {mathdoc},
     volume = {138},
     number = {4},
     year = {2009},
     doi = {10.4064/aa138-4-4},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/aa138-4-4/}
}