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%I #21 Sep 08 2022 08:46:23
%S 1,2,10,26,86,210,594,1394,3530,8006,18842,41258,92190,195714,419538,
%T 867050,1797568,3625758,7311382,14431294,28416514,55010142,106101558,
%U 201814518,382213566,715473554,1333083950,2459265058,4515151234,8218572030,14888270366,26766878302
%N Expansion of Product_{i>=1, j>=1, k>=1, l>=1} (1 + x^(i*j*k*l))/(1 - x^(i*j*k*l)).
%C Convolution of the sequences A280486 and A280487.
%H Seiichi Manyama, <a href="/A321240/b321240.txt">Table of n, a(n) for n = 0..10000</a>
%F G.f.: Product_{k>=1} ((1 + x^k)/(1 - x^k))^A007426(k).
%t 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 (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 (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 Cf. A007426, A015128, A280486, A280487, A301554, A305050.
%K nonn
%O 0,2
%A _Seiichi Manyama_, Nov 01 2018
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