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 A015814 #25 Dec 25 2023 01:51:24 %S A015814 1,3,5,6,7,11,14,15,17,23,24,28,31,33,35,47,51,53,54,55,69,71,77,87, %T A015814 94,107,110,127,155,170,174,191,195,209,254,261,265,285,315,322,383, %U A015814 385,395,399,406,423,429,431,510,564,609,636,644,647,649,672,713 %N A015814 Numbers k such that phi(k + 1) divides sigma(k). %H A015814 Amiram Eldar, <a href="/A015814/b015814.txt">Table of n, a(n) for n = 1..10000</a> %t A015814 Select[Range[1000], Divisible[DivisorSigma[1, #], EulerPhi[1 + #]] &] (* _David Nacin_, Mar 01 2012 *) %o A015814 (PARI) is(n)=!(sigma(n)%eulerphi(n+1)) \\ _Charles R Greathouse IV_, Sep 25 2012 %Y A015814 Cf. A000010, A000203, A015834, A020492. %K A015814 nonn %O A015814 1,2 %A A015814 _Robert G. Wilson v_ %E A015814 Definition corrected by _David Nacin_, Mar 01 2012