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 A042859 Denominators of continued fraction convergents to sqrt(960). 3
 1, 1, 61, 62, 3781, 3843, 234361, 238204, 14526601, 14764805, 900414901, 915179706, 55811197261, 56726376967, 3459393815281, 3516120192248, 214426605350161, 217942725542409, 13290990137894701, 13508932863437110, 823826961944121301, 837335894807558411 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS The following remarks assume an offset of 1. This is the sequence of Lehmer numbers U_n(sqrt(R),Q) for the parameters R = 60 and Q = -1. This is a strong divisibility sequence, that is, gcd(a(n),a(m)) = a(gcd(n,m)) for all positive integers n and m. Consequently, this is a divisibility sequence: if n divides m then a(n) divides a(m). - Peter Bala, May 26 2014 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..200 Eric W. Weisstein, MathWorld: Lehmer Number Index entries for linear recurrences with constant coefficients, signature (0,62,0,-1). FORMULA G.f.: -(x^2-x-1) / ((x^2-8*x+1)*(x^2+8*x+1)). - Colin Barker, Dec 25 2013 a(n) = 62*a(n-2) - a(n-4) for n>3. - Vincenzo Librandi, Dec 25 2013 From Peter Bala, May 26 2014: (Start)   The following remarks assume an offset of 1:   Let alpha = sqrt(15) + 4 and beta = sqrt(15) - 4 be the roots of the equation x^2 - sqrt(60)*x - 1 = 0. Then a(n) = (alpha^n - beta^n)/(alpha - beta) for n odd, while a(n) = (alpha^n - beta^n)/(alpha^2 - beta^2) for n even.   a(n) = product {k = 1..floor((n-1)/2)} ( 60 + 4*cos^2(k*Pi/n) ). Recurrence equations: a(0) = 0, a(1) = 1 and for n >= 1, a(2*n) = a(2*n - 1) + a(2*n - 2) and a(2*n + 1) = 60*a(2*n) + a(2*n - 1). (End) MATHEMATICA Denominator[Convergents[Sqrt, 30]] (* Vincenzo Librandi, Dec 25 2013 *) PROG (MAGMA) I:=[1, 1, 61, 62]; [n le 4 select I[n] else 62*Self(n-2)-Self(n-4): n in [1..50]]; // Vincenzo Librandi, Dec 25 2013 CROSSREFS Cf. A042858, A040929. Cf. A002530. Sequence in context: A122568 A075028 A258158 * A258157 A114085 A195378 Adjacent sequences:  A042856 A042857 A042858 * A042860 A042861 A042862 KEYWORD nonn,frac,easy AUTHOR N. J. A. Sloane, Dec 11 1999 EXTENSIONS More terms from Colin Barker, Dec 25 2013 STATUS approved

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Last modified August 8 23:02 EDT 2020. Contains 336300 sequences. (Running on oeis4.)