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 A364209 #28 Jul 23 2023 13:03:54
%S A364209 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2,1,1,1,2,1,1,1,2,1,1,1,2,1,1,1,2,1,1,
%T A364209 1,2,1,1,1,2,1,1,1,2,1,1,1,2,2,1,1,2,1,1,1,3,1,1,1,2,1,1,2,2,1,1,1,2,
%U A364209 1,2,1,2,1,1,1,2,2,1,1,2,1,1,1,3,1,1,1,2,1,1,2,2,1,1,1,2,1,2,1,3
%N A364209 Number of divisors of n of the form 3*k+1 that are at most sqrt(n).
%F A364209 G.f.: Sum_{k>=0} x^(3*k+1)^2 / (1 - x^(3*k+1)).
%t A364209 Table[Count[Divisors[n], _?(# <= Sqrt[n] && MemberQ[{1}, Mod[#, 3]] &)], {n, 100}]
%t A364209 nmax = 100; CoefficientList[Series[Sum[x^(3 k + 1)^2/(1 - x^(3 k + 1)), {k, 0, nmax}], {x, 0, nmax}], x] // Rest
%Y A364209 Cf. A001817, A038548, A364357.
%K A364209 nonn
%O A364209 1,16
%A A364209 _Ilya Gutkovskiy_, Jul 21 2023