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 A163667 #17 Dec 04 2019 18:17:26 %S A163667 30,264,714,3080,3828,6678,10098,12648,21318,22152,24882,44660,49938, %T A163667 61344,86304,94944,118296,129504,130356,147560,183396,199386,201756, %U A163667 207264,216936,248710,258440,265914,275196,290290,321204,505164,628776,706266,706836 %N A163667 Numbers n such that sigma(n) = 9*phi(n). %C A163667 This sequence is a subsequence of A011257 because sqrt(phi(n)*sigma(n)) = 3*phi(n). %C A163667 If 2^p-1 and 2*3^k-1 are two primes greater than 5 then n = 2^(p-2)*(2^p-1)*3^(k-1)*(2*3^k-1) (the product of two relatively prime terms 2^(p-2)*(2^p-1) and 3^(k-1)*(2*3^k-1) of A011257) is in the sequence. The proof is easy. %H A163667 Amiram Eldar, <a href="/A163667/b163667.txt">Table of n, a(n) for n = 1..10000</a> (calculated using data from Jud McCranie, terms 1..1000 from Donovan Johnson) %H A163667 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 A163667 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 A163667 Select[Range[700000],DivisorSigma[1,# ]==9EulerPhi[ # ]&] %o A163667 (PARI) is(n)=sigma(n)==9*eulerphi(n) \\ _Charles R Greathouse IV_, May 09 2013 %Y A163667 Cf. A000010, A000043, A000203, A000668, A003307, A011257, A079363. %K A163667 easy,nonn %O A163667 1,1 %A A163667 _M. F. Hasler_ and _Farideh Firoozbakht_, Aug 09 2009