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 A152771 #20 Apr 24 2021 09:55:10
%S A152771 0,0,1,2,3,5,5,8,8,11,9,17,11,17,17,22,15,28,17,31,25,29,21,45,26,35,
%T A152771 33,45,27,57,29,52,41,47,41,74,35,53,49,75,39,81,41,73,67,65,45,105,
%U A152771 52,82,65,87,51,105,65,105,73,83,57,145
%N A152771 a(n) = sigma(n) - 2*d(n) + 1.
%H A152771 Ivan Neretin, <a href="/A152771/b152771.txt">Table of n, a(n) for n = 1..10000</a>
%F A152771 a(n) = A000203(n) - 2*A000005(n) + 1 = A000203(n) - A114003(n) = A088580(n) - A062011(n). - _Omar E. Pol_, Sep 30 2017
%F A152771 G.f.: Sum_{k>=1} x^(3*k) / (1 - x^k)^2. - _Ilya Gutkovskiy_, Apr 24 2021
%t A152771 Table[DivisorSigma[1, n] - 2 DivisorSigma[0, n] + 1, {n, 60}] (* _Ivan Neretin_, Sep 30 2017 *)
%o A152771 (PARI) a(n) = sigma(n) - 2*numdiv(n) + 1; \\ _Michel Marcus_, Sep 30 2017
%Y A152771 Cf. A000005, A000203, A152770, A152772.
%K A152771 nonn,easy
%O A152771 1,4
%A A152771 _Omar E. Pol_, Dec 14 2008