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 A112399 #21 Dec 19 2021 10:26:12
%S A112399 1,1,0,0,-1,0,-1,-2,-2,-1,-1,-2,-2,-3,-2,-3,-1,-4,-2,-5,-4,-3,-1,-6,
%T A112399 -3,-4,-3,-5,-1,-6,-3,-7,-5,-5,-3,-7,-1,-5,-3,-6,0,-9,-2,-7,-6,-6,-2,
%U A112399 -11,-4,-9,-5,-7,-2,-12,-5,-8,-5,-5,0,-13,-1,-7,-6,-8,-4,-12,-1,-8,-5,-10,-2,-14,-3,-8,-9,-9,-4,-14,-3,-12,-7,-8,-3,-17
%N A112399 a(n) = Sum_{k=1..n, gcd(k,n)=1} mu(k), where mu(k) = A008683(k) (the Moebius function).
%e A112399 The positive integers <= 10 and coprime to 10 are 1, 3, 7 and 9. So a(10) = mu(1) + mu(3) + mu(7) + mu(9) = 1 - 1 - 1 + 0 = -1.
%t A112399 quetMu[n_] := Sum[KroneckerDelta[GCD[i, n], 1] MoebiusMu[i], {i, n}]; Table[quetMu[n], {n, 85}] (* _Alonso del Arte_, Nov 28 2011 *)
%o A112399 (PARI) a(n)=sum(k=1,n,if(gcd(n,k)==1,moebius(k),0)) \\ Lambert Herrgesell, Dec 09 2005
%Y A112399 Cf. A008683.
%K A112399 sign
%O A112399 1,8
%A A112399 _Leroy Quet_, Dec 06 2005
%E A112399 More terms from Lambert Herrgesell and _Matthew Conroy_, Dec 09 2005