@article{JIS_2008__11_1_a5,
     author = {De Koninck, Jean-Marie and Luca, Florian},
     title = {Positive integers $n$ such that $\sigma(\varphi(n))=\sigma(n)$},
     journal = {Journal of integer sequences},
     publisher = {mathdoc},
     volume = {11},
     number = {1},
     year = {2008},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/JIS_2008__11_1_a5/}
}