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 A171260 #18 Jul 29 2024 19:01:27 %S A171260 840,11880,12180,25080,32130,67830,79170,172260,282744,312840,363660, %T A171260 569160,596904,634410,696696,843780,846090,959310,996840,1119690, %U A171260 1201560,1402440,1542840,1607340,1929312,2104440,2247210,2363790,3309240,3368040,3883680 %N A171260 Numbers n such that sigma(n) = 15*phi(n) (where sigma=A000203, phi=A000010). %H A171260 Amiram Eldar, <a href="/A171260/b171260.txt">Table of n, a(n) for n = 1..10000</a> (calculated using data from Jud McCranie, terms 1..1000 from Donovan Johnson) %H A171260 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 A171260 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 A171260 Select[Range[10^6], DivisorSigma[1, #] == 15 * EulerPhi[#] &] (* _Amiram Eldar_, Dec 04 2019 *) %o A171260 (PARI) for(k=1,3e6, sigma(k) - 15*eulerphi(k) || print1(k", ")); %Y A171260 Cf. A062699, A068391, A068390, A136547, A104900, A136540, A104901, A163667, A171256, A171257, A104902, A171258, A171259, A104903. %K A171260 nonn %O A171260 1,1 %A A171260 _Farideh Firoozbakht_ and _M. F. Hasler_, Mar 19 2010