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 A117208 #9 Feb 13 2015 09:08:28
%S A117208 1,-1,1,0,0,1,-1,2,-1,1,0,1,0,1,0,0,2,-1,2,0,1,0,1,1,1,0,1,1,0,2,1,1,
%T A117208 1,0,2,0,3,0,0,2,0,3,0,3,-1,2,0,4,1,1,3,-3,5,1,3,0,2,-1,2,4,2,4,-5,6,
%U A117208 -1,2,7,-2,1,-1,4,3,5,2,-2,1,1,8,2,4,-1,-3,4,9,4,-2,4,-7,6,7,10,-1,-3,-1,1,11,4,8,-15,2,5,7,13,1,-9,-7,9
%N A117208 G.f. A(x) satisfies (1-x) = product_{n>=1} A(x^n).
%C A117208 Self-convolution inverse is A117209.
%H A117208 Paul D. Hanna, <a href="/A117208/b117208.txt">Table of n, a(n) for n = 0..1000</a>
%F A117208 G.f.: A(x) = exp( -Sum_{n>=1} A023900(n)*x^n/n ), where A023900 is the Dirichlet inverse of Euler totient function.
%F A117208 Euler transform of the negative of the Möbius function. - _Stuart Clary_, Apr 15 2006
%F A117208 G.f.: A(x) = product_{k>=1}(1 - x^k)^mu(k) where mu(k) is the Möbius function, A008683. - _Stuart Clary_, Apr 15 2006
%t A117208 nmax = 106; CoefficientList[ Series[ Product[ (1 - x^k)^(MoebiusMu[k]), {k, 1, nmax} ], {x, 0, nmax} ], x ] (* _Stuart Clary_, Apr 15 2006 *)
%o A117208 (PARI) {a(n)=polcoeff(exp(-sum(k=1,n+1,sumdiv(k,d,d*moebius(d))*x^k/k)+x*O(x^n)),n)}
%Y A117208 Cf. A023900 (l.g.f.), A117209 (inverse); variants: A117210, A117211, A117212.
%K A117208 sign
%O A117208 0,8
%A A117208 _Paul D. Hanna_, Mar 03 2006