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 A266941 Expansion of Product_{k>=1} 1 / (1 - k*x^k)^k. 15
 1, 1, 5, 14, 42, 103, 289, 690, 1771, 4206, 10142, 23449, 54786, 123528, 279480, 619206, 1366405, 2969071, 6425534, 13727775, 29187555, 61439660, 128620370, 267044222, 551527679, 1130806020, 2306746335, 4676096006, 9432394144, 18920266428, 37776372312 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS This sequence is obtained from the generalized Euler transform in A266964 by taking f(n) = n, g(n) = n. - Seiichi Manyama, Nov 18 2017 LINKS Seiichi Manyama, Table of n, a(n) for n = 0..6086 (terms 0..1000 from Vaclav Kotesovec) FORMULA From Vaclav Kotesovec, Jan 08 2016: (Start) a(n) ~ c * n^2 * 3^(n/3), where c = 3278974684037157122864203.021982619109776972432419491714093... if mod(n,3)=0 c = 3278974684037157122864202.999526122508793149896683112820555... if mod(n,3)=1 c = 3278974684037157122864203.001231135511323719311281438384212... if mod(n,3)=2 (End) In closed form, a(n) ~ (Product_{k>=4}((1 - k/3^(k/3))^(-k)) / ((1 - 2/3^(2/3))^2 * (1 - 1/3^(1/3))) + Product_{k>=4}((1 - (-1)^(2*k/3)*k/3^(k/3))^(-k)) / ((-1)^(2*n/3) * ((1 + 2*(-1)^(1/3)/3^(2/3))^2 * (1 - (-1)^(2/3)/3^(1/3)))) + Product_{k>=4}((1 - (-1)^(4*k/3)*k/3^(k/3))^(-k)) / ((-1)^(4*n/3) * ((1 + (-1/3)^(1/3)) * (1 - 2*(-1/3)^(2/3))^2))) * 3^(n/3) * n^2 / 54. - Vaclav Kotesovec, Apr 24 2017 a(0) = 1 and a(n) = (1/n) * Sum_{k=1..n} (Sum_{d|k} d^(2+k/d)) * a(n-k) for n > 0. - Seiichi Manyama, Nov 02 2017 MATHEMATICA nmax = 40; CoefficientList[Series[Product[1/(1-k*x^k)^k, {k, 1, nmax}], {x, 0, nmax}], x] nmax = 40; s = 1 - x; Do[s *= Sum[Binomial[k, j]*(-1)^j*k^j*x^(j*k), {j, 0, nmax/k}]; s = Expand[s]; s = Take[s, Min[nmax + 1, Exponent[s, x] + 1, Length[s]]]; , {k, 2, nmax}]; CoefficientList[Series[1/s, {x, 0, nmax}], x] (* Vaclav Kotesovec, Aug 27 2018 *) CROSSREFS Cf. A006906, A265758, A266891, A266942, A266964, A266971. Sequence in context: A032249 A129937 A147978 * A034549 A232492 A180774 Adjacent sequences:  A266938 A266939 A266940 * A266942 A266943 A266944 KEYWORD nonn AUTHOR Vaclav Kotesovec, Jan 06 2016 STATUS approved

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Last modified July 17 20:45 EDT 2019. Contains 325109 sequences. (Running on oeis4.)