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 A321261 #4 Nov 01 2018 18:21:24
%S A321261 1,0,1,1,17,2,859,131,105508,40907,72916903,6834168,228239366293,
%T A321261 27616985835,2050004858009336,352807044193881,87173272463714343166,
%U A321261 6798224808203572198,18318379579349549499397403,1187836799227050499295342,11258903016282277676462826232428
%N A321261 a(n) = [x^n] Product_{k>=1} (1 + x^k)^(sigma_n(k)-k^n).
%F A321261 a(n) = [x^n] exp(Sum_{k>=1} ( Sum_{d|k} (-1)^(k/d+1)*d*(sigma_n(d) - d^n) ) * x^k/k).
%t A321261 Table[SeriesCoefficient[Product[(1 + x^k)^(DivisorSigma[n, k] - k^n), {k, 1, n}], {x, 0, n}], {n, 0, 20}]
%t A321261 Table[SeriesCoefficient[Exp[Sum[Sum[(-1)^(k/d + 1) d (DivisorSigma[n, d] - d^n), {d, Divisors[k]}] x^k/k, {k, 1, n}]], {x, 0, n}], {n, 0, 20}]
%Y A321261 Cf. A281268, A318844, A319107, A321042, A321258, A321260.
%K A321261 nonn
%O A321261 0,5
%A A321261 _Ilya Gutkovskiy_, Nov 01 2018