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 A346558 #11 Sep 30 2021 05:35:57
%S A346558 1,4,9,20,35,78,133,280,531,1070,2057,4212,8203,16534,32865,65840,
%T A346558 131087,262818,524305,1049740,2097459,4196390,8388629,16782024,
%U A346558 33554575,67117102,134218809,268452212,536870939,1073777010,2147483677,4295033440,8589938775,17180000318,34359739085
%N A346558 a(n) = Sum_{d|n} phi(n/d) * (2^d - 1).
%F A346558 G.f.: Sum_{k>=1} phi(k) * x^k / ((1 - x^k) * (1 - 2*x^k)).
%F A346558 a(n) = Sum_{k=1..n} (2^gcd(n,k) - 1).
%F A346558 a(n) = n * (A000031(n) - 1) = n * A008965(n).
%F A346558 Dirichlet convolution of A000225 and A000010. - _R. J. Mathar_, Sep 30 2021
%t A346558 Table[Sum[EulerPhi[n/d] (2^d - 1), {d, Divisors[n]}], {n, 1, 35}]
%t A346558 nmax = 35; CoefficientList[Series[Sum[EulerPhi[k] x^k/((1 - x^k) (1 - 2 x^k)), {k, 1, nmax}], {x, 0, nmax}], x] // Rest
%o A346558 (PARI) a(n) = sumdiv(n, d, eulerphi(n/d)*(2^d - 1)); \\ _Michel Marcus_, Sep 17 2021
%Y A346558 Cf. A000010, A000031, A000225, A008965, A034738, A038199, A053635.
%K A346558 nonn
%O A346558 1,2
%A A346558 _Ilya Gutkovskiy_, Sep 17 2021