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 A171258 #21 Jul 29 2024 19:01:17 %S A171258 630,5544,11160,18810,27000,57000,80388,161820,178020,182880,242820, %T A171258 265608,388620,391500,447678,465192,522522,671760,690120,711000, %U A171258 775170,826500,901170,1051830,1102290,1157130,1418160,1578330,1679400,1812384,1874520,1993824 %N A171258 Numbers n such that sigma(n) = 13*phi(n) (where sigma=A000203, phi=A000010). %H A171258 Amiram Eldar, <a href="/A171258/b171258.txt">Table of n, a(n) for n = 1..10000</a> (calculated using data from Jud McCranie, terms 1..1000 from Donovan Johnson) %H A171258 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 A171258 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 A171258 Select[Range[2*10^6],DivisorSigma[1,#]==13EulerPhi[#]&] (* _Harvey P. Dale_, Mar 29 2018 *) %o A171258 (PARI) for(k=1,2e6, sigma(k) - 13*eulerphi(k) || print1(k", ")); %Y A171258 Cf. A062699, A068391, A068390, A136547, A104900, A136540, A104901, A163667, A171256, A171257, A104902, A171259, A171260, A104903. %K A171258 nonn %O A171258 1,1 %A A171258 _Farideh Firoozbakht_ and _M. F. Hasler_, Mar 19 2010