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 A321263 #4 Nov 01 2018 18:21:36
%S A321263 1,0,1,1,18,3,926,264,146255,64190,138356840,22816773,509079790798,
%T A321263 108923489863,6757117812676818,1403337110700033,474610323092906351464,
%U A321263 52144014892723916074,130074987349483695192896881,14487112805054799566652854,132992779975091800967037313578152
%N A321263 a(n) = [x^n] 1/(1 - Sum_{k>=1} k^n*x^(2*k)/(1 - x^k)).
%F A321263 a(n) = [x^n] 1/(1 - Sum_{k>=1} (sigma_n(k) - k^n)*x^k).
%F A321263 a(n) = [x^n] 1/(1 - Sum_{k>=1} (k^n - J_n(k))*x^k/(1 - x^k)), where J_() is the Jordan function.
%t A321263 Table[SeriesCoefficient[1/(1 - Sum[k^n x^(2 k)/(1 - x^k), {k, 1, n}]), {x, 0, n}], {n, 0, 20}]
%t A321263 Table[SeriesCoefficient[1/(1 - Sum[(DivisorSigma[n, k] - k^n) x^k, {k, 1, n}]), {x, 0, n}], {n, 0, 20}]
%t A321263 Table[SeriesCoefficient[1/(1 - Sum[(k^n - Sum[d^n MoebiusMu[k/d], {d, Divisors[k]}]) x^k/(1 - x^k), {k, 1, n}]), {x, 0, n}], {n, 0, 20}]
%Y A321263 Cf. A321190, A321258, A321260, A321261, A321262.
%K A321263 nonn
%O A321263 0,5
%A A321263 _Ilya Gutkovskiy_, Nov 01 2018