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 A220418 Express 1 - x - x^2 - x^3 - x^4 - ... as product (1 + g(1)*x) * (1 + g(2)*x^2) *(1 + g(3)*x^3) * ... and use a(n) = - g(n). 27
 1, 1, 2, 3, 6, 8, 18, 27, 54, 84, 186, 296, 630, 1008, 2106, 3711, 7710, 12924, 27594, 48528, 97902, 173352, 364722, 647504, 1340622, 2382660, 4918482, 9052392, 18512790, 33361776, 69273666, 127198287, 258155910, 475568220, 981288906, 1814542704, 3714566310 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS This is the PPE (power product expansion) of A153881 (with offset 0). When p is prime, a(p) = (2^p-2)/p (A064535). From Petros Hadjicostas, Oct 04 2019: (Start) This sequence appears as an example in Gingold and Knopfmacher (1995) starting at p. 1223. In Section 3 of Gingold and Knopfmacher (1995), it is proved that, if f(z) = Product_{n >= 1} (1 + g(n))*z^n = 1/(Product_{n >= 1} (1 - h(n))*z^n), then g(2*n - 1) = h(2*n - 1) and Sum_{d|n} (1/d)*h(n/d)^d = -Sum_{d|n} (1/d)*(-g(n/d))^d. The same results were proved more than ten years later by Alkauskas (2008, 2009). [If we let a(n) = -g(n), then Alkauskas works with f(z) = Product_{n >= 1} (1 - a(n))*z^n; i.e., a(2*n - 1) = -h(2*n - 1) etc.] The PPE of 1/(1 - x - x^2 - x^3 - x^4 - ...) is given in A290261, which is also studied in Gingold and Knopfmacher (1995, p. 1234). (End) LINKS Alois P. Heinz, Table of n, a(n) for n = 1..2000 Giedrius Alkauskas, One curious proof of Fermat's little theorem, arXiv:0801.0805 [math.NT], 2008. Giedrius Alkauskas, A curious proof of Fermat's little theorem, Amer. Math. Monthly 116(4) (2009), 362-364. H. Gingold, H. W. Gould, and Michael E. Mays, Power Product Expansions, Utilitas Mathematica 34 (1988), 143-161. H. Gingold and A. Knopfmacher, Analytic properties of power product expansions, Canad. J. Math. 47 (1995), 1219-1239. W. Lang, Recurrences for the general problem. FORMULA g(1) = -1 and for k > 1, g(k) satisfies Sum_{d|k} (1/d)*(-g(k/d))^d = (2^k - 1)/k, where a(k) = -g(k). - Gevorg Hmayakyan, Jun 05 2016 [Corrected by Petros Hadjicostas, Oct 04 2019. See p. 1224 in Gingold and Knopfmacher (1995).] From Petros Hadjicostas, Oct 04 2019: (Start) a(2*n - 1) = A290261(2*n - 1) for n >= 1 because A290261 gives the PPE of 1/(1 - x - x^2 - x^3 - ...) = (1 - x)/(1 - 2*x). Define (A(m,n): n,m >= 1) by A(m=1,n) = -1 for n >= 1, A(m,n) = 0 for m > n >= 1 (upper triangular), and A(m,n) = A(m-1,n) - A(m-1,m-1) * A(m,n-m+1) for n >= m >= 2. Then a(n) = A(n,n). [Theorem 3 in Gingold et al. (1988).] (End) MAPLE b:= proc(n, i) option remember; `if`(n=0 or i<1, 1,       b(n, i-1)+a(i)*b(n-i, min(n-i, i)))     end: a:= proc(n) option remember; 2^n-b(n, n-1) end: seq(a(n), n=1..40);  # Alois P. Heinz, Jun 22 2018 MATHEMATICA b[n_, i_] := b[n, i] = If[n == 0 || i < 1, 1, b[n, i - 1] + a[i]*b[n - i, Min[n - i, i]]]; a[n_] := a[n] = 2^n - b[n, n - 1] ; Array[a, 40] (* Jean-François Alcover, Jul 09 2018, after Alois P. Heinz *) PROG (PARI) a(m) = {default(seriesprecision, m+1); gk = vector(m); pol = 1 + sum(n=1, m, -x^n); gk[1] = polcoeff( pol, 1); for (k=2, m, pol = taylor(pol/(1+gk[k-1]*x^(k-1)), x); gk[k] = polcoeff(pol, k, x); ); for (k=1, m, print1(-gk[k], ", "); ); } CROSSREFS Cf. A064535, A147541, A153881, A157162, A170908, A170909, A170910, A170911, A170912, A170913, A170914, A170915, A170916, A170917, A220420, A273866, A290261. Sequence in context: A110448 A005508 A022542 * A064450 A217137 A248824 Adjacent sequences:  A220415 A220416 A220417 * A220419 A220420 A220421 KEYWORD nonn AUTHOR Michel Marcus, Dec 14 2012 EXTENSIONS Name edited by Petros Hadjicostas, Oct 04 2019 STATUS approved

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Last modified May 7 20:36 EDT 2021. Contains 343652 sequences. (Running on oeis4.)