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 A238271 #13 Jul 07 2023 13:19:58
%S A238271 1,8,1,9,9,5,3,8,6,7,0,2,6,3,3,8,8,7,8,2,7,8,0,0,1,0,0,3,0,0,5,6,5,5,
%T A238271 7,3,2,2,6,3,4,4,9,8,0,1,3,5,3,8,3,0,6,1,7,5,9,2,4,9,4,7,7,1,6,3,2,4,
%U A238271 2,0,4,8,3,6,8,5,0,5,4,1,6,4,2,2,8,9,8,3,9,5,7,7,6,4,9,2,3,9,9,0,2,6,9,9,4
%N A238271 Decimal expansion of sum(n>=1, mu(n)/3^n ).
%C A238271 Suggested by a posting to SeqFan list by Alonso Del Arte at 15:35 on Aug 09 2012.
%e A238271 =0.1819953867026338878278001003005655732263449801353830617592494771...
%t A238271 RealDigits[ Sum[ N[ MoebiusMu[n] 3^-n, 128], {n, 300}], 10, 111][[1]]
%Y A238271 Cf. A008683, A238270, A181673 & A238273.
%K A238271 nonn,cons,easy
%O A238271 0,2
%A A238271 _Robert G. Wilson v_, Feb 21 2014