cp's OEIS Frontend

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.

A321068 a(n) = [x^n] Product_{k>=1} ((1 - x^k)/(1 + x^k))^sigma_n(k).

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%I A321068 #17 Oct 28 2018 10:47:07
%S A321068 1,-2,-8,-22,294,24982,1372372,10145326,-38651841784,-21995644478504,
%T A321068 -5088041946350856,29713279339187796814,155715351422115081062330,
%U A321068 370606511915720675179342334,-12360092915168107023209454901320
%N A321068 a(n) = [x^n] Product_{k>=1} ((1 - x^k)/(1 + x^k))^sigma_n(k).
%H A321068 Seiichi Manyama, <a href="/A321068/b321068.txt">Table of n, a(n) for n = 0..80</a>
%t A321068 Table[SeriesCoefficient[Product[((1 - x^k)/(1 + x^k))^DivisorSigma[n, k], {k, 1, n}], {x, 0, n}], {n, 0, 15}] (* _Vaclav Kotesovec_, Oct 27 2018 *)
%o A321068 (PARI) {a(n) = polcoeff(prod(k=1, n, ((1-x^k+x*O(x^n))/(1+x^k+x*O(x^n)))^sigma(k, n)), n)}
%Y A321068 Cf. A320908, A320971, A320972, A321042, A321057.
%K A321068 sign
%O A321068 0,2
%A A321068 _Seiichi Manyama_, Oct 26 2018