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 A161219 #12 Jun 24 2021 05:56:58
%S A161219 4,6,8,12,16,28,40,72,120,216,376,704,1264,2364,4384,8232,15424,29204,
%T A161219 55192,104976,199760,381492,729448,1398504,2684368,5162856,9942136,
%U A161219 19175160,37025584,71585136,138547336,268439592,520602352,1010588256,1963413664,3817763800
%N A161219 a(n) = (1/n) * Sum_{d|n} phi(n/d)*2^(d+1).
%H A161219 Andrew Howroyd, <a href="/A161219/b161219.txt">Table of n, a(n) for n = 1..1000</a>
%F A161219 G.f.: -2 * Sum_{k>=1} phi(k) * log(1 - 2*x^k) / k. - _Ilya Gutkovskiy_, Apr 15 2021
%F A161219 a(n) = 2*A000031(n). - _Hugo Pfoertner_, Jun 24 2021
%o A161219 (PARI) a(n) = sumdiv(n, d, eulerphi(n/d)*2^(d+1))/n; \\ _Michel Marcus_, Apr 15 2021
%Y A161219 Cf. A000031, A053635, A160619, A161217.
%K A161219 nonn
%O A161219 1,1
%A A161219 _N. J. A. Sloane_, Nov 21 2009