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 A321240 #21 Sep 08 2022 08:46:23 %S A321240 1,2,10,26,86,210,594,1394,3530,8006,18842,41258,92190,195714,419538, %T A321240 867050,1797568,3625758,7311382,14431294,28416514,55010142,106101558, %U A321240 201814518,382213566,715473554,1333083950,2459265058,4515151234,8218572030,14888270366,26766878302 %N A321240 Expansion of Product_{i>=1, j>=1, k>=1, l>=1} (1 + x^(i*j*k*l))/(1 - x^(i*j*k*l)). %C A321240 Convolution of the sequences A280486 and A280487. %H A321240 Seiichi Manyama, <a href="/A321240/b321240.txt">Table of n, a(n) for n = 0..10000</a> %F A321240 G.f.: Product_{k>=1} ((1 + x^k)/(1 - x^k))^A007426(k). %t A321240 With[{nmax=50}, CoefficientList[Series[Product[(1 + x^(i*j*k*l))/(1 - x^(i*j*k*l)), {i,1,nmax}, {j,1,nmax/i}, {k,1,nmax/i/j}, {l,1,nmax/i/j/k}], {x,0,nmax}], x]] (* _G. C. Greubel_, Nov 01 2018 *) %o A321240 (PARI) m=50; x='x+O('x^m); Vec(prod(k=1,m, ((1+x^k)/(1-x^k))^ sumdiv(k, d, numdiv(k/d)*numdiv(d)))) \\ _G. C. Greubel_, Nov 01 2018 %o A321240 (Magma) m:=50; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!( (&*[(&*[(&*[(&*[(1+x^(i*j*k*l))/(1-x^(i*j*k*l)): i in [1..m]]): j in [1..m]]): k in [1..m]]): l in [1..m]]))); // _G. C. Greubel_, Nov 01 2018 %Y A321240 Cf. A007426, A015128, A280486, A280487, A301554, A305050. %K A321240 nonn %O A321240 0,2 %A A321240 _Seiichi Manyama_, Nov 01 2018