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 A372664 #10 May 09 2024 07:00:54
%S A372664 1,9,21,55,93,163,241,383,507,709,915,1205,1497,1907,2220,2794,3306,
%T A372664 3966,4610,5438,6075,7113,8067,9245,10272,11742,12900,14552,16086,
%U A372664 17798,19552,21894,23532,26082,27933,30589,33105,36307,38619,41945,45049,48459,51875
%N A372664 a(n) = Sum_{j=1..n} Sum_{k=1..n} phi(2*j*k) / phi(k).
%H A372664 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TotientFunction.html">Totient Function</a>.
%t A372664 Table[Sum[Sum[EulerPhi[2*j*k], {j, 1, n}]/EulerPhi[k], {k, 1, n}], {n, 1, 50}] (* _Vaclav Kotesovec_, May 09 2024 *)
%o A372664 (PARI) a(n) = sum(j=1, n, sum(k=1, n, eulerphi(2*j*k)/eulerphi(k)));
%Y A372664 Cf. A000010, A372636, A372665.
%K A372664 nonn
%O A372664 1,2
%A A372664 _Seiichi Manyama_, May 09 2024