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 A340140 #17 Jan 06 2021 17:48:08
%S A340140 -1,0,0,-2,0,-7,0,-6,-6,-13,0,-13,0,-19,-22,-22,0,-19,0,-23,-32,-31,0,
%T A340140 -81,-20,-37,-24,-33,0,-21,0,-78,-52,-49,-58,-183,0,-55,-62,-147,0,
%U A340140 -29,0,-53,-52,-67,0,-321,-42,-53,-82,-63,0,-223,-94,-213,-92,-85,0,-591,0,-91,-74,-278,-112,-45,0,-83,-112,-45,0,-733
%N A340140 a(1) = -1, for n > 1, a(n) = Sum_{d|n, d<n} A340197(n/d) * a(d).
%C A340140 This seems to differ from 1-A318833(n) at the points given by A033987.
%H A340140 Antti Karttunen, <a href="/A340140/b340140.txt">Table of n, a(n) for n = 1..16384</a>
%F A340140 a(1) = -1, for n > 1, a(n) = Sum_{d|n, d<n} A340197(n/d) * a(d).
%o A340140 (PARI)
%o A340140 A023900(n) = factorback(apply(p -> 1-p, factor(n)[, 1]));
%o A340140 A318833(n) = (n+A023900(n));
%o A340140 A340197(n) = if(1==n,1,sumdiv(n,d,if(d<n,(A318833(n/d)-1)*A340197(d),0)));
%o A340140 A340140(n) = if(1==n, -1, sumdiv(n, d, if(d<n, A340197(n/d)*A340140(d), 0)));
%Y A340140 Cf. A023900, A033987, A318833, A340197, A340367.
%K A340140 sign,less
%O A340140 1,4
%A A340140 _Antti Karttunen_, Jan 05 2021