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 A015834 #17 Sep 09 2019 01:23:28 %S A015834 1,2,4,5,6,9,10,13,14,20,21,30,32,34,43,45,54,55,65,68,70,104,109,114, %T A015834 129,132,140,151,153,160,176,183,203,234,245,252,279,314,340,370,407, %U A015834 434,441,539,550,580,589,620,635,644,741,765,798,806,845,860,883 %N A015834 Numbers k such that phi(k) | sigma(k + 1). %H A015834 Ivan Neretin, <a href="/A015834/b015834.txt">Table of n, a(n) for n = 1..1000</a> %t A015834 Select[Range[3000], Divisible[DivisorSigma[1, 1 + #], EulerPhi[#]] &] (* _David Nacin_, Mar 03 2012 *) %o A015834 (PARI) is(n)=!(sigma(n+1)%eulerphi(n)) \\ _Charles R Greathouse IV_, Sep 25 2012 %K A015834 nonn %O A015834 1,2 %A A015834 _Robert G. Wilson v_ %E A015834 a(1) = 1 inserted by _Ivan Neretin_, Feb 05 2017