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 A343465 #7 Apr 16 2021 15:41:48
%S A343465 3,-3,11,-21,51,-119,315,-831,2195,-5883,16107,-44357,122643,-341487,
%T A343465 956635,-2690841,7596483,-21522347,61171659,-174342165,498112275,
%U A343465 -1426403751,4093181691,-11767920107,33891544419,-97764009003,282429537947,-817028472645,2366564736723,-6863037262207
%N A343465 a(n) = -(1/n) * Sum_{d|n} phi(n/d) * (-3)^d.
%F A343465 G.f.: Sum_{k>=1} phi(k) * log(1 + 3*x^k) / k.
%F A343465 a(n) = -(1/n) * Sum_{k=1..n} (-3)^gcd(n,k).
%F A343465 Product_{n>=1} 1 / (1 - x^n)^a(n) = g.f. for A032308.
%F A343465 Product_{n>=1} (1 - x^n)^a(n) = g.f. for A261582.
%t A343465 Table[-(1/n) Sum[EulerPhi[n/d] (-3)^d, {d, Divisors[n]}], {n, 1, 30}]
%t A343465 nmax = 30; CoefficientList[Series[Sum[EulerPhi[k] Log[1 + 3 x^k]/k, {k, 1, nmax}], {x, 0, nmax}], x] // Rest
%Y A343465 Cf. A000010, A001867, A032308, A038064, A074763, A261582, A343466, A343467.
%K A343465 sign
%O A343465 1,1
%A A343465 _Ilya Gutkovskiy_, Apr 16 2021