A171257 - OEIS

%I #19 Jul 29 2024 19:01:41

%S 2580,16770,18630,28896,35970,61404,66024,147576,163944,215124,224010,

%T 296184,399126,408672,443394,464340,476010,574308,856086,862752,

%U 868428,931224,957348,1004910,1110186,1496610,1721720,1723290,1833348,1971288,2139852,2234790

%N Numbers n such that sigma(n) = 11*phi(n) (where sigma=A000203, phi=A000010).

%H Amiram Eldar, <a href="/A171257/b171257.txt">Table of n, a(n) for n = 1..10000</a> (calculated using data from Jud McCranie, terms 1..1000 from Donovan Johnson)

%H Kevin A. Broughan and Daniel Delbourgo, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL16/Broughan/broughan26.html">On the Ratio of the Sum of Divisors and Euler’s Totient Function I</a>, Journal of Integer Sequences, Vol. 16 (2013), Article 13.8.8.

%H Kevin A. Broughan and Qizhi Zhou, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL17/Broughan/bro32.html">On the Ratio of the Sum of Divisors and Euler's Totient Function II</a>, Journal of Integer Sequences, Vol. 17 (2014), Article 14.9.2.

%t Select[Range[10^6], DivisorSigma[1, #] == 11 * EulerPhi[#] &] (* _Amiram Eldar_, Dec 04 2019 *)

%o (PARI) for(k=1,2e6, sigma(k) - 11*eulerphi(k) || print1(k", "));

%Y Cf. A062699, A068391, A068390, A136547, A104900, A136540, A104901, A163667, A171256, A104902, A171258, A171259, A171260, A104903.

%K nonn

%O 1,1

%A _Farideh Firoozbakht_ and _M. F. Hasler_, Mar 19 2010