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 A364211 #9 Jul 14 2023 08:47:52
%S A364211 1,3,9,33,126,527,2233,9783,43409,195378,887785,4069297,18780049,
%T A364211 87194199,406901134,1907353533,8975758273,42385547227,200773540297,
%U A364211 953674414158,4541306270097,21674416725855,103660251783289,496705375169547,2384185791015751,11462431696965147,55189485903168409
%N A364211 a(n) = (1/(4*n)) * Sum_{d|n} 5^(n/d-1) * phi(5*d).
%F A364211 G.f.: (-1/4) * Sum_{k>0} phi(5*k) * log(1-5*x^k)/(5*k).
%t A364211 a[n_] := DivisorSum[n, 5^(n/#-1)*EulerPhi[5*#]/(4*n) &]; Array[a, 25] (* _Amiram Eldar_, Jul 14 2023 *)
%o A364211 (PARI) a(n) = sumdiv(n, d, 5^(n/d-1)*eulerphi(5*d))/(4*n);
%Y A364211 Cf. A000010, A343492, A359100, A359101.
%Y A364211 Cf. A000013, A364210, A364212.
%K A364211 nonn
%O A364211 1,2
%A A364211 _Seiichi Manyama_, Jul 13 2023