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 A364210 #9 Jul 14 2023 09:03:16
%S A364210 1,2,4,8,17,44,105,278,733,1978,5369,14792,40881,113934,318884,896948,
%T A364210 2532161,7174862,20390553,58114072,166037460,475473286,1364393897,
%U A364210 3922640132,11297181473,32588043882,94143179560,272342824320,788854912241,2287679406940,6641649422409
%N A364210 a(n) = (1/(2*n)) * Sum_{d|n} 3^(n/d-1) * phi(3*d).
%F A364210 G.f.: (-1/2) * Sum_{k>0} phi(3*k) * log(1-3*x^k)/(3*k).
%t A364210 a[n_] := DivisorSum[n, 3^(n/#-1)*EulerPhi[3*#]/(2*n) &]; Array[a, 30] (* _Amiram Eldar_, Jul 14 2023 *)
%o A364210 (PARI) a(n) = sumdiv(n, d, 3^(n/d-1)*eulerphi(3*d))/(2*n);
%Y A364210 Cf. A000010, A034754, A195459, A327625.
%Y A364210 Cf. A000013, A364211, A364212.
%K A364210 nonn
%O A364210 1,2
%A A364210 _Seiichi Manyama_, Jul 13 2023