This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A171257 #19 Jul 29 2024 19:01:41 %S A171257 2580,16770,18630,28896,35970,61404,66024,147576,163944,215124,224010, %T A171257 296184,399126,408672,443394,464340,476010,574308,856086,862752, %U A171257 868428,931224,957348,1004910,1110186,1496610,1721720,1723290,1833348,1971288,2139852,2234790 %N A171257 Numbers n such that sigma(n) = 11*phi(n) (where sigma=A000203, phi=A000010). %H A171257 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 A171257 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 A171257 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 A171257 Select[Range[10^6], DivisorSigma[1, #] == 11 * EulerPhi[#] &] (* _Amiram Eldar_, Dec 04 2019 *) %o A171257 (PARI) for(k=1,2e6, sigma(k) - 11*eulerphi(k) || print1(k", ")); %Y A171257 Cf. A062699, A068391, A068390, A136547, A104900, A136540, A104901, A163667, A171256, A104902, A171258, A171259, A171260, A104903. %K A171257 nonn %O A171257 1,1 %A A171257 _Farideh Firoozbakht_ and _M. F. Hasler_, Mar 19 2010