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 A041025 Denominators of continued fraction convergents to sqrt(17). 25
 1, 8, 65, 528, 4289, 34840, 283009, 2298912, 18674305, 151693352, 1232221121, 10009462320, 81307919681, 660472819768, 5365090477825, 43581196642368, 354014663616769, 2875698505576520, 23359602708228929, 189752520171407952, 1541379764079492545 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS a(2*n+1) with b(2*n+1) := A041024(2*n+1), n>=0, give all (positive integer) solutions to Pell equation b^2 - 17*a^2 = +1, a(2*n) with b(2*n) := A041024(2*n), n>=0, give all (positive integer) solutions to Pell equation b^2 - 17*a^2 = -1 (cf. Emerson reference). Bisection: a(2*n)= T(2*n+1,sqrt(17))/sqrt(17)= A078988(n), n>=0 and a(2*n+1)=8*S(n-1,66),n>=0, with T(n,x), resp. S(n,x), Chebyshev's polynomials of the first, resp. second kind. S(-1,x)=0. See A053120, resp. A049310. - Wolfdieter Lang, Jan 10 2003 Sqrt(17) = 8/2 + 8/65 + 8/(65*4289) + 8/(4289*283009) + ... . - Gary W. Adamson, Dec 26 2007 a(p) == ((p-1)/2)) mod p for odd primes p. - Gary W. Adamson, Feb 22 2009 For positive n, a(n) equals the permanent of the n X n tridiagonal matrix with 8's along the main diagonal and 1's along the superdiagonal and the subdiagonal. - John M. Campbell, Jul 08 2011 De Moivre's formula: a(n) = (r^n-s^n)/(r-s), for r>s, gives sequences with integers if r and s are conjugates. With r=4+sqrt(17) and s=4-sqrt(17), a(n+1)/a(n) converges to r=4+sqrt(17). - Sture Sjöstedt, Nov 11 2011 a(n) equals the number of words of length n on alphabet {0,1,...,8} avoiding runs of zeros of odd lengths. - Milan Janjic, Jan 28 2015 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 D. Birmajer, J. B. Gil, M. D. Weiner, n the Enumeration of Restricted Words over a Finite Alphabet , J. Int. Seq. 19 (2016) # 16.1.3, Example 8 E. I. Emerson, Recurrent Sequences in the Equation DQ^2=R^2+N, Fib. Quart., 7 (1969), pp. 231-242, Thm. 1, p. 233. Sergio Falcón and Ángel Plaza, The k-Fibonacci sequence and the Pascal 2-triangle, Chaos, Solitons & Fractals 2007; 33(1): 38-49. S. Falcón & Á. Plaza, On k-Fibonacci sequences and polynomials and their derivatives, Chaos, Solitons & Fractals (2007). M. Janjic, On Linear Recurrence Equations Arising from Compositions of Positive Integers, Journal of Integer Sequences, Vol. 18 (2015), Article 15.4.7. Tanya Khovanova, Recursive Sequences Index entries for linear recurrences with constant coefficients, signature (8,1). FORMULA G.f.: 1/(1 - 8*x - x^2). a(n) = ((-i)^n)*S(n, 8*i), with S(n, x) := U(n, x/2) Chebyshev's polynomials of the second kind and i^2 = -1. See A049310. a(n) = F(n, 8), the n-th Fibonacci polynomial evaluated at x=8. - T. D. Noe, Jan 19 2006 From Sergio Falcon, Sep 24 2007: (Start) a(n) = ((4 + sqrt(17))^n - (4 - sqrt(17))^n)/(2*sqrt(17)); a(n) = Sum_{i=0..floor((n-1)/2)} binomial(n-1-i,i)*8^(n-1-2i). (End) Let T be the 2 X 2 matrix [0, 1; 1, 8]. Then T^n * [1, 0] = [a(n-2), a(n-1)]. - Gary W. Adamson, Dec 26 2007 a(n) = 8*a(n-1) + a(n-2), n>1; a(0)=1, a(1)=8. - Philippe Deléham, Nov 20 2008 Sum_{n>=0} (-1)^n/(a(n)*a(n+1)) = sqrt(17) - 4. - Vladimir Shevelev, Feb 23 2013 MATHEMATICA a=0; lst={}; s=0; Do[a=s-(a-1); AppendTo[lst, a]; s+=a*8, {n, 3*4!}]; lst (* Vladimir Joseph Stephan Orlovsky, Oct 27 2009 *) CoefficientList[Series[1/(-z^2 - 8 z + 1), {z, 0, 200}], z] (* Vladimir Joseph Stephan Orlovsky, Jun 23 2011 *) Denominator[Convergents[Sqrt, 30]] (* Harvey P. Dale, Aug 15 2011 *) LinearRecurrence[{8, 1}, {1, 8}, 50] (* Sture Sjöstedt, Nov 11 2011 *) PROG (Sage) [lucas_number1(n, 8, -1) for n in range(1, 20)] # Zerinvary Lajos, Apr 25 2009 (Magma) I:=[1, 8]; [n le 2 select I[n] else 8*Self(n-1)+Self(n-2): n in [1..25]]; // Vincenzo Librandi, Feb 23 2013 (PARI) Vec(1/(1-8*x-x^2)+O(x^99)) \\ Charles R Greathouse IV, Dec 09 2014 CROSSREFS Cf. A041024, A040012. Cf. A000045, A000129, A006190, A001076, A052918, A005668, A054413, A243399. Sequence in context: A033118 A033126 A022039 * A163459 A081190 A189431 Adjacent sequences:  A041022 A041023 A041024 * A041026 A041027 A041028 KEYWORD nonn,cofr,easy AUTHOR STATUS approved

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Last modified October 4 12:36 EDT 2022. Contains 357239 sequences. (Running on oeis4.)