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 A321240 Expansion of Product_{i>=1, j>=1, k>=1, l>=1} (1 + x^(i*j*k*l))/(1 - x^(i*j*k*l)). 2
 1, 2, 10, 26, 86, 210, 594, 1394, 3530, 8006, 18842, 41258, 92190, 195714, 419538, 867050, 1797568, 3625758, 7311382, 14431294, 28416514, 55010142, 106101558, 201814518, 382213566, 715473554, 1333083950, 2459265058, 4515151234, 8218572030, 14888270366, 26766878302 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Convolution of the sequences A280486 and A280487. LINKS Seiichi Manyama, Table of n, a(n) for n = 0..10000 FORMULA G.f.: Product_{k>=1} ((1 + x^k)/(1 - x^k))^A007426(k). MATHEMATICA 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 *) PROG (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 (Magma) m:=50; R:=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 CROSSREFS Cf. A007426, A015128, A280486, A280487, A301554, A305050. Sequence in context: A324914 A025589 A084182 * A322201 A099583 A328743 Adjacent sequences: A321237 A321238 A321239 * A321241 A321242 A321243 KEYWORD nonn AUTHOR Seiichi Manyama, Nov 01 2018 STATUS approved

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Last modified March 21 08:05 EDT 2023. Contains 361393 sequences. (Running on oeis4.)