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 A015837 #21 Sep 09 2019 01:23:31 %S A015837 1,2,3,4,5,9,10,12,13,18,21,22,25,28,36,38,40,42,45,52,55,58,60,90,93, %T A015837 108,112,117,130,152,153,156,175,180,182,187,208,222,226,228,246,258, %U A015837 264,280,306,310,313,380,396,468,490,504,532,592,609,628,700,715 %N A015837 Numbers k such that phi(k) | sigma(k + 2). %H A015837 Ivan Neretin, <a href="/A015837/b015837.txt">Table of n, a(n) for n = 1..1000</a> %t A015837 Select[Range[3000], Divisible[DivisorSigma[1, 2 + #], EulerPhi[#]] &] (* _David Nacin_, Mar 03 2012 *) %o A015837 (PARI) isok(n) = !(sigma(n+2) % eulerphi(n)); \\ _Michel Marcus_, Feb 05 2017 %K A015837 nonn %O A015837 1,2 %A A015837 _Robert G. Wilson v_ %E A015837 a(1) = 1 inserted by _Ivan Neretin_, Feb 05 2017