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 A098018 #16 Sep 04 2017 23:29:12
%S A098018 0,1,-1,0,0,-1,1,-1,-1,1,1,-3,0,1,0,0,0,-2,0,-1,0,3,1,-5,0,1,0,0,0,-1,
%T A098018 -1,-1,0,2,2,-3,0,0,0,-1,0,-2,-1,1,0,2,1,-5,1,1,-1,1,0,-2,1,0,-1,2,1,
%U A098018 -5,0,-1,1,-1,0,2,-1,0,0,3,-1,-6,0,0,1,-1,2,1,-1,-1,0,1,1,-5,0,1,0,1,0,-3,1,2,-2,3,1,-5,0,0,0,-1,0,-1,-1,-1,2
%N A098018 a(n) = Sum_{k|n, k>=2} mu(k-1), where mu() is the Moebius function.
%H A098018 Michael De Vlieger, <a href="/A098018/b098018.txt">Table of n, a(n) for n = 1..10000</a>
%e A098018 12's divisors >=2 are 2, 3, 4, 6 and 12. So a(12) = mu(1) + mu(2) + mu(3) + mu(5) + mu(11) = 1 - 1 - 1 - 1 - 1 = -3.
%t A098018 f[n_] := Plus @@ MoebiusMu[ Drop[ Divisors[n], 1] - 1]; Table[ f[n], {n, 105}] (* _Robert G. Wilson v_, Nov 01 2004 *)
%t A098018 Table[DivisorSum[n, MoebiusMu[# - 1] &, # > 1 &], {n, 105}] (* _Michael De Vlieger_, Sep 04 2017 *)
%o A098018 (PARI) a(n)=sumdiv(n,k,if(k>1,moebius(k-1))) \\ _Charles R Greathouse IV_, Feb 07 2013
%Y A098018 Cf. A008683, A098035.
%K A098018 sign
%O A098018 1,12
%A A098018 _Leroy Quet_, Oct 24 2004
%E A098018 More terms from _Robert G. Wilson v_, Nov 01 2004