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 A320649 Expansion of 1/(1 - Sum_{k>=1} k^2*x^k/(1 - x^k)). 2
 1, 1, 6, 21, 82, 294, 1116, 4103, 15326, 56833, 211454, 785441, 2920058, 10851016, 40331874, 149892024, 557098510, 2070493098, 7695228038, 28600012305, 106294901116, 395055313662, 1468262641770, 5456942875386, 20281270503914, 75377349437075, 280147395367820 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Invert transform of A001157. LINKS N. J. A. Sloane, Transforms FORMULA G.f.: 1/(1 + x * (d/dx) log(Product_{k>=1} (1 - x^k)^k)). a(0) = 1; a(n) = Sum_{k=1..n} sigma_2(k)*a(n-k). MAPLE a:=series(1/(1-add(k^2*x^k/(1-x^k), k=1..100)), x=0, 27): seq(coeff(a, x, n), n=0..26); # Paolo P. Lava, Apr 02 2019 MATHEMATICA nmax = 26; CoefficientList[Series[1/(1 - Sum[k^2 x^k/(1 - x^k), {k, 1, nmax}]), {x, 0, nmax}], x] nmax = 26; CoefficientList[Series[1/(1 + x D[Log[Product[(1 - x^k)^k, {k, 1, nmax}]], x]), {x, 0, nmax}], x] a[0] = 1; a[n_] := a[n] = Sum[DivisorSigma[2, k] a[n - k], {k, 1, n}]; Table[a[n], {n, 0, 26}] CROSSREFS Cf. A000219, A001157, A180305. Sequence in context: A134927 A108306 A199115 * A219596 A182251 A191597 Adjacent sequences:  A320646 A320647 A320648 * A320650 A320651 A320652 KEYWORD nonn AUTHOR Ilya Gutkovskiy, Oct 18 2018 STATUS approved

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Last modified February 26 03:24 EST 2020. Contains 332272 sequences. (Running on oeis4.)