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 A356346 #7 Aug 05 2022 06:16:55
%S A356346 2,8,48,188,1196,3044,23636,75116,366836,1105860,8160180,18976804,
%T A356346 143784004,384483604,1625423764,6434066884,43771766404,98222578204,
%U A356346 734437326604,1837209557164,8296304050444,29337293687644,210472769694844,468453599159644,2996665727914684
%N A356346 a(n) = Sum_{k=1..n} binomial(2*k, k) * phi(k), where phi is the Euler totient function.
%C A356346 The average value of a(n) is sqrt(n) * 2^(2*n+3) / Pi^(5/2).
%t A356346 Table[Sum[Binomial[2*k, k]*EulerPhi[k], {k, 1, n}], {n, 1, 30}]
%o A356346 (PARI) a(n) = sum(k=1, n, binomial(2*k, k) * eulerphi(k)); \\ _Michel Marcus_, Aug 05 2022
%Y A356346 Cf. A000010, A002088, A306988.
%K A356346 nonn
%O A356346 1,1
%A A356346 _Vaclav Kotesovec_, Aug 04 2022