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 A015793 #16 Aug 06 2014 04:40:04 %S A015793 6,15,21,24,30,33,39,42,51,57,66,69,78,84,87,93,96,102,108,111,114, %T A015793 120,123,129,138,141,159,174,175,177,183,186,201,213,219,220,222,237, %U A015793 246,249,258,267,282,291,303,309,318,321,327,339,350,354,366 %N A015793 Numbers n such that phi(n) + 4 divides sigma(n). %H A015793 Vincenzo Librandi, <a href="/A015793/b015793.txt">Table of n, a(n) for n = 1..1300</a> %t A015793 Select[Range[400],Divisible[DivisorSigma[1,#],EulerPhi[#]+4]&] (* _Harvey P. Dale_, Aug 05 2014 *) %o A015793 (PARI) is(n)=!(sigma(n)%eulerphi(n+4)) \\ _Charles R Greathouse IV_, Sep 25 2012 %K A015793 nonn %O A015793 1,1 %A A015793 _Robert G. Wilson v_