Geodesic
On the ratio of the sum of divisors and Euler's totient function. II.
Journal of integer sequences, Tome 17 (2014) no. 9.

Voir la notice de l'article provenant de la source Electronic Library of Mathematics

Summary: 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 
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     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},
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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/