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 A015843 #21 Sep 09 2019 01:23:35 %S A015843 1,2,6,9,10,16,18,22,28,30,33,42,64,65,71,72,82,87,90,114,130,136,156, %T A015843 182,198,208,215,280,294,336,380,390,403,451,616,660,683,755,777,964, %U A015843 990,1168,1260,1267,1330,1342,1348,1480,1638,1744,1953,2025,2074,2088 %N A015843 Numbers k such that phi(k) | sigma(k + 5). %H A015843 Ivan Neretin, <a href="/A015843/b015843.txt">Table of n, a(n) for n = 1..1000</a> %t A015843 Select[Range[3000], Divisible[DivisorSigma[1, 5 + #], EulerPhi[#]] &] (* _David Nacin_, Mar 03 2012 *) %o A015843 (PARI) isok(n) = !(sigma(n+5) % eulerphi(n)); \\ _Michel Marcus_, Feb 05 2017 %K A015843 nonn %O A015843 1,2 %A A015843 _Robert G. Wilson v_ %E A015843 a(1) = 1 inserted by _Ivan Neretin_, Feb 05 2017