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 A307704 #12 Feb 29 2024 13:30:58
%S A307704 -1,1,-1,2,0,4,2,6,3,7,5,11,9,13,9,14,12,18,16,22,18,22,20,28,25,29,
%T A307704 25,31,29,37,35,41,37,41,37,46,44,48,44,52,50,58,56,62,56,60,58,68,65,
%U A307704 71,67,73,71,79,75,83,79,83,81,93,91,95,89,96,92,100,98,104,100,108
%N A307704 Expansion of (1/(1 - x)) * Sum_{k>=1} (-x)^k/(1 - (-x)^k).
%H A307704 Amiram Eldar, <a href="/A307704/b307704.txt">Table of n, a(n) for n = 1..10000</a>
%H A307704 László Tóth, <a href="https://www.emis.de/journals/JIS/VOL20/Toth/toth25.html">Alternating Sums Concerning Multiplicative Arithmetic Functions</a>, Journal of Integer Sequences, Vol. 20 (2017), Article 17.2.1.
%F A307704 a(n) = Sum_{k=1..n} (-1)^k*A000005(k).
%F A307704 a(n) = n*log(n)/2 + (gamma - log(2) - 1/2)*n + O(n^(131/416 + eps)) (Tóth, 2017). - _Amiram Eldar_, Oct 14 2022
%t A307704 nmax = 70; Rest[CoefficientList[Series[1/(1 - x) Sum[(-x)^k/(1 - (-x)^k), {k, 1, nmax}], {x, 0, nmax}], x]]
%t A307704 Table[Sum[(-1)^k DivisorSigma[0, k], {k, 1, n}], {n, 1, 70}]
%t A307704 Accumulate[Array[(-1)^#*DivisorSigma[0, #] &, 70]] (* _Amiram Eldar_, Oct 14 2022 *)
%Y A307704 Cf. A000005, A006218, A051950, A059851, A068762, A068773, A092405, A263084 (bisection).
%Y A307704 Cf. A001620 (gamma), A002162.
%K A307704 sign
%O A307704 1,4
%A A307704 _Ilya Gutkovskiy_, Apr 22 2019