Geodesic
On the ratio of the sum of divisors and Euler's totient function. II.
Journal of integer sequences, Tome 17 (2014) no. 9
We find the form of all solutions to $\phi (n) | \sigma (n)$ with three or fewer prime factors, except when the quotient is 4 and $n$ is even.
Classification : 11A25, 11A41, 54H99, 11N60, 11N25, 11N64
Keywords: sum of divisors, Euler's totient function 
@article{JIS_2014__17_9_a2,
     author = {Broughan,  Kevin A. and Zhou,  Qizhi},
     title = {On the ratio of the sum of divisors and {Euler's} totient function. {II.}},
     journal = {Journal of integer sequences},
     year = {2014},
     volume = {17},
     number = {9},
     zbl = {1358.11015},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/JIS_2014__17_9_a2/}
}
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Broughan,  Kevin A.; Zhou,  Qizhi. On the ratio of the sum of divisors and Euler's totient function. II.. Journal of integer sequences, Tome 17 (2014) no. 9. http://geodesic.mathdoc.fr/item/JIS_2014__17_9_a2/