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 A045755 8-fold factorials: a(n) = Product_{k=0..n-1} (8*k+1). 28
 1, 1, 9, 153, 3825, 126225, 5175225, 253586025, 14454403425, 939536222625, 68586144251625, 5555477684381625, 494437513909964625, 47960438849266568625, 5035846079172989705625, 569050606946547836735625 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS G. C. Greubel, Table of n, a(n) for n = 0..330 FORMULA a(n+1) = (8*n+1)(!^8). a(n) = Sum_{k=0..n} (-8)^(n-k)*A048994(n, k); A048994 = Stirling-1 numbers. E.g.f.: (1-8*x)^(-1/8). G.f.: 1+x/(1-9x/(1-8x/(1-17x/(1-16x/(1-25x/(1-24x/(1-33x/(1-32x/(1-... (continued fraction). - Philippe Deléham, Jan 07 2012 a(n) = (-7)^n*Sum_{k=0..n} (8/7)^k*s(n+1,n+1-k), where s(n,k) are the Stirling numbers of the first kind, A048994. [Mircea Merca, May 03 2012] G.f.: 1/Q(0) where Q(k) = 1 - x*(8*k+1)/(1 - x*(8*k+8)/Q(k+1) ); (continued fraction). - Sergei N. Gladkovskii, Mar 20 2013 G.f.: 2/G(0), where G(k)= 1 + 1/(1 - 2*x*(8*k+1)/(2*x*(8*k+1) - 1 + 16*x*(k+1)/G(k+1))); (continued fraction). - Sergei N. Gladkovskii, May 30 2013 G.f.: G(0)/2, where G(k)= 1 + 1/(1 - x*(8*k+1)/(x*(8*k+1) + 1/G(k+1))); (continued fraction). - Sergei N. Gladkovskii, Jun 05 2013 a(n) = 8^n * Gamma(n + 1/8) / Gamma(1/8). - Artur Jasinski,Aug 23 2016 a(n) ~ sqrt(2*Pi) * 8^n * n^(n - 3/8)/(Gamma(1/8)*exp(n)). - Ilya Gutkovskiy, Sep 10 2016 D-finite with recurrence: a(n) +(-8*n+7)*a(n-1)=0. - R. J. Mathar, Jan 17 2020 MAPLE a := n->product(8*k+1), k=0..(n-1)); MATHEMATICA Table[8^n*Pochhammer[1/8, n], {n, 0, 20}] (* G. C. Greubel, Nov 11 2019 *) PROG (PARI) a(n)=prod(k=0, n, 8*k+1); (MAGMA) [1] cat [(&*[8*j+1: j in [0..n-1]]): n in [1..20]]; // G. C. Greubel, Nov 11 2019 (Sage) [product( (8*j+1) for j in (0..n-1)) for n in (0..20)] # G. C. Greubel, Nov 11 2019 (GAP) List([0..20], n-> Product([0..n-1], j-> 8*j+1) ); # G. C. Greubel, Nov 11 2019 CROSSREFS Cf. k-fold factorials : A000142, A001147, A007559, A007696, A008548, A008542, A045754. Cf. A051187, A113135. Sequence in context: A217822 A217823 A113391 * A009037 A012148 A193540 Adjacent sequences:  A045752 A045753 A045754 * A045756 A045757 A045758 KEYWORD nonn AUTHOR EXTENSIONS Additional comments from Philippe Deléham and Paul D. Hanna, Oct 29 2005 Edited by N. J. A. Sloane, Oct 14 2008 at the suggestion of Artur Jasinski. STATUS approved

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Last modified January 25 20:36 EST 2021. Contains 340427 sequences. (Running on oeis4.)