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 A356343 #7 Aug 05 2022 06:13:09
%S A356343 2,10,61,288,1723,6524,37441,158504,737019,2867500,15200293,56951428,
%T A356343 291648771,1141099348,4686310739,19016248192,95307214595,358297247772,
%U A356343 1748879020425,6725041736572,27649247188159,108460437728204,522912325647543,1966622896068784,8831400010510925
%N A356343 a(n) = Sum_{k=1..n} binomial(2*n, k) * phi(k), where phi is the Euler totient function.
%F A356343 a(n) ~ 3 * n * 4^n / Pi^2.
%t A356343 Table[Sum[Binomial[2*n, k]*EulerPhi[k], {k, 1, n}], {n, 1, 30}]
%o A356343 (PARI) a(n) = sum(k=1, n, binomial(2*n, k) * eulerphi(k)); \\ _Michel Marcus_, Aug 05 2022
%Y A356343 Cf. A000010, A002088, A306988.
%K A356343 nonn
%O A356343 1,1
%A A356343 _Vaclav Kotesovec_, Aug 04 2022