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 A065568 #11 Aug 30 2019 04:19:50
%S A065568 1,4,10,22,42,84,154,298,568,1108,2142,4254,8362,16636,33076,66004,
%T A065568 131556,262974,525136,1050016,2098756,4196962,8391288,16782312,
%U A065568 33559612,67118176,134227594,268453714,536889198,1073777718,2147519572
%N A065568 Sum over all subsets of {1,..,n} of the GCD of the subset.
%H A065568 Amiram Eldar, <a href="/A065568/b065568.txt">Table of n, a(n) for n = 1..3321</a>
%t A065568 Sum[Plus @@ GCD @@@ KSubsets[Range[n], m], {m, n}] (* or *)
%t A065568 Table[Sum[Plus@@(EulerPhi[Divisors[k]] 2^(k/Divisors[k]))/2, {k, n}], {n, 42}]
%Y A065568 Row sums of A065567, first differences equal A034738,
%K A065568 nonn
%O A065568 1,2
%A A065568 _Wouter Meeussen_, Nov 30 2001