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 A041041 Denominators of continued fraction convergents to sqrt(26). 16
 1, 10, 101, 1020, 10301, 104030, 1050601, 10610040, 107151001, 1082120050, 10928351501, 110365635060, 1114584702101, 11256212656070, 113676711262801, 1148023325284080, 11593909964103601, 117087122966320090, 1182465139627304501, 11941738519239365100 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Generalized Fibonacci sequence. Sqrt(26) = 10/2 + 10/101 + 10/(101*10301) + 10/(10301*1050601) + ... - Gary W. Adamson, Jun 13 2008 For positive n, a(n) equals the permanent of the n X n tridiagonal matrix with 10's along the main diagonal and 1's along the superdiagonal and the subdiagonal. - John M. Campbell, Jul 08 2011 a(n) equals the number of words of length n on alphabet {0, 1, ..., 10} avoiding runs of zeros of odd lengths. - Milan Janjic, Jan 28 2015 From Bruno Berselli, May 03 2018: (Start) Numbers k for which m*k^2 + (-1)^k is a perfect square: m =  2: 0, 1, 2, 5, 12, 29, 70, 169, ...   (A000129); m =  3: 0, 4, 56, 780, 10864, 151316, ...  (4*A007655); m =  5: 0, 1, 4, 17, 72, 305, 1292, ...    (A001076); m =  6: 0, 2, 20, 198, 1960, 19402, ...    (A001078); m =  7: 0, 48, 12192, 3096720, ...         (2*A175672); m =  8: 0, 6, 204, 6930, 235416, ...       (A082405); m = 10: 0, 1, 6, 37, 228, 1405, 8658, ...  (A005668); m = 11: 0, 60, 23880, 9504180, ...         [°]; m = 12: 0, 2, 28, 390, 5432, 75658, ...    (A011944); m = 13: 0, 5, 180, 6485, 233640, ...       (5*A041613); m = 14: 0, 4, 120, 3596, 107760, ...       (A068204); m = 15: 0, 8, 496, 30744, 1905632, ...     [°]; m = 17: 0, 1, 8, 65, 528, 4289, 34840, ... (A041025); m = 18: 0, 4, 136, 4620, 156944, ...       (A202299); m = 19: 0, 13260, 1532829480, ...          [°]; m = 20: 0, 2, 36, 646, 11592, 208010, ...  (A207832); m = 21: 0, 12, 1320, 145188, ...           (A174745); m = 22: 0, 42, 16548, 6519870, ...         (A174766); m = 23: 0, 240, 552480, 1271808720, ...    [°]; m = 24: 0, 10, 980, 96030, 9409960, ...    (A168520); m = 26: 0, 1, 10, 101, 1020, 10301, ...    (this sequence); m = 27: 0, 260, 702520, 1898208780, ...    [°]; m = 28: 0, 24, 6096, 1548360, ...          (A175672); m = 29: 0, 13, 1820, 254813, 35675640, ... [°]; m = 30: 0, 2, 44, 966, 21208, 465610, ...  (2*A077421), etc. [°] apparently without related sequences in OEIS. (End) LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..200 Sergio Falcon and Ángel Plaza, On the Fibonacci k-numbers, Chaos, Solitons & Fractals 2007; 32(5): 1615-24. Sergio Falcon and Ángel Plaza, The k-Fibonacci sequence and the Pascal 2-triangle Chaos, Solitons & Fractals 2007; 33(1): 38-49. Sergio Falcon and Ángel 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 (10,1). FORMULA G.f.: 1/(1 - 10*x - x^2). a(n) = 10*a(n-1) + a(n-2), n>=1; a(-1):=0, a(0)=1. a(n) = S(n, 10*I)*(-I)^n with I^2:=-1 and S(n, x)=U(n, x/2) Chebyshev's polynomials of the second kind. See A049310. a(n) = (ap^(n+1) - am^(n+1))/(ap-am) with ap = 5+sqrt(26), am = -1/ap = 5-sqrt(26). a(n) = F(n+1, 10), the (n+1)-th Fibonacci polynomial evaluated at x=10. - T. D. Noe, Jan 19 2006 a(n) = Sum_{i=0..floor(n/2)} binomial(n-i,i)*10^(n-2*i). - Sergio Falcon, Sep 24 2007 MAPLE seq(combinat:-fibonacci(n+1, 10), n=0..19); # Peter Luschny, May 04 2018 MATHEMATICA Denominator[Convergents[Sqrt[26], 30]] (* Vincenzo Librandi, Dec 10 2013 *) LinearRecurrence[{10, 1}, {1, 10}, 30] (* G. C. Greubel, Jan 24 2018 *) PROG (Sage) [lucas_number1(n, 10, -1) for n in xrange(1, 19)] # Zerinvary Lajos, Apr 26 2009 (PARI) x='x+O('x^30); Vec(1/(1-10*x-x^2)) \\ G. C. Greubel, Jan 24 2018 (MAGMA) I:=[1, 10]; [n le 2 select I[n] else 10*Self(n-1) + Self(n-2): n in [1..30]]; // G. C. Greubel, Jan 24 2018 CROSSREFS Cf. squares A099374. Cf. A041040, A000045, A000129, A006190, A001076, A052918, A005668, A054413, A041025, A099371, A243399. Sequence in context: A180175 A267526 A261199 * A163461 A081192 A288809 Adjacent sequences:  A041038 A041039 A041040 * A041042 A041043 A041044 KEYWORD nonn,frac,easy AUTHOR EXTENSIONS Extended by T. D. Noe, May 23 2011 STATUS approved

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Last modified December 17 00:28 EST 2018. Contains 318191 sequences. (Running on oeis4.)