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 A318368 #9 Aug 26 2018 11:09:31
%S A318368 1,3,13,27,81,183,449,987,2317,5043,11265,24399,53249,114243,245853,
%T A318368 523227,1114113,2357175,4980737,10480587,22020557,46126083,96468993,
%U A318368 201302799,419430481,872361987,1811941645,3757981275,7784628225,16105886823,33285996545,68718951387,141733932045
%N A318368 a(n) = Sum_{d|n} (-1)^(n/d+1)*d*2^(d-1).
%F A318368 G.f.: Sum_{k>=1} k*2^(k-1)*x^k/(1 + x^k).
%F A318368 L.g.f.: log(Product_{k>=1} (1 + x^k)^(2^(k-1))) = Sum_{n>=1} a(n)*x^n/n.
%F A318368 a(n) ~ n * 2^(n-1). - _Vaclav Kotesovec_, Aug 25 2018
%t A318368 Table[Sum[(-1)^(n/d + 1) d 2^(d - 1), {d, Divisors[n]}], {n, 33}]
%t A318368 nmax = 33; Rest[CoefficientList[Series[Sum[k 2^(k - 1) x^k/(1 + x^k), {k, 1, nmax}], {x, 0, nmax}], x]]
%t A318368 nmax = 33; Rest[CoefficientList[Series[Log[Product[(1 + x^k)^(2^(k - 1)), {k, 1, nmax}]], {x, 0, nmax}], x] Range[0, nmax]]
%o A318368 (PARI) a(n) = sumdiv(n, d, (-1)^(n/d+1)*d*2^(d-1)); \\ _Michel Marcus_, Aug 25 2018
%Y A318368 Cf. A001787, A054599, A083413, A098407.
%K A318368 nonn
%O A318368 1,2
%A A318368 _Ilya Gutkovskiy_, Aug 24 2018