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 A073540 #19 May 10 2022 11:17:13 %S A073540 4,6,8,9,16,24,25,27,28,32,40,49,64,81,121,125,128,169,224,243,256, %T A073540 289,343,360,361,496,512,529,625,672,729,841,864,936,961,1024,1331, %U A073540 1369,1681,1849,2016,2048,2176,2187,2197,2209,2401,2809,3125,3481,3721,4096 %N A073540 Composite numbers k such that k/phi(k) - sigma(k)/k has numerator equal to 1. %H A073540 Amiram Eldar, <a href="/A073540/b073540.txt">Table of n, a(n) for n = 1..10000</a> %t A073540 Select[Range[4100], ! PrimeQ[#] && Numerator[#/EulerPhi[#] - DivisorSigma[1, #]/#] == 1 &] (* _Jayanta Basu_, Jul 01 2013 *) %o A073540 (PARI) isok(k) = if (!isprime(k), numerator(k/eulerphi(k) - sigma(k)/k) == 1); \\ _Michel Marcus_, May 10 2022 %Y A073540 Cf. A000010, A000203, A017665, A017666, A076512, A109395. %K A073540 easy,nonn %O A073540 1,1 %A A073540 _Benoit Cloitre_, Aug 27 2002