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 A098991 #8 Mar 16 2017 04:19:33
%S A098991 5,9,13,15,21,27,33,35,37,39,50,55,57,61,65,73,91,93,95,111,114,115,
%T A098991 121,122,133,141,143,145,147,155,157,170,177,183,185,189,193,195,201,
%U A098991 205,209,213,215,217,219,231,235,247,253,259,261,277,285,295,299,301,313
%N A098991 Numbers n where A098035(n)=0.
%H A098991 Indranil Ghosh, <a href="/A098991/b098991.txt">Table of n, a(n) for n = 1..935</a> (terms < 5000)
%F A098991 Sum_{k|n} mu(k+1), where mu() is Moebius function.
%t A098991 f[n_] := Plus @@ MoebiusMu[Divisors[n] + 1]; Select[ Range[319], f[ # ] == 0 &]
%o A098991 (PARI) a(n) = sumdiv(n, k, moebius(k + 1));
%o A098991 for(n=1, 320, if(a(n) == 0, print1(n,", "))) \\ _Indranil Ghosh_, Mar 16 2017
%Y A098991 Cf. A098035.
%K A098991 nonn
%O A098991 1,1
%A A098991 _Leroy Quet_ and _Robert G. Wilson v_, Nov 05 2004