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A041799 Denominators of continued fraction convergents to sqrt(420). 2
1, 2, 81, 164, 6641, 13446, 544481, 1102408, 44640801, 90384010, 3660001201, 7410386412, 300075457681, 607561301774, 24602527528641, 49812616359056, 2017107181890881, 4084026980140818, 165378186387523601, 334840399755188020, 13558994176595044401 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..200

Index entries for linear recurrences with constant coefficients, signature (0,82,0,-1).

FORMULA

G.f.: -(x^2-2*x-1) / (x^4-82*x^2+1). - Colin Barker, Nov 25 2013

a(n) = 82*a(n-2) - a(n-4) for n>3. - Vincenzo Librandi, Dec 24 2013

MATHEMATICA

Denominator[Convergents[Sqrt[420], 30]] (* Vincenzo Librandi, Dec 24 2013 *)

PROG

(MAGMA) I:=[1, 2, 81, 164]; [n le 4 select I[n] else 82*Self(n-2)-Self(n-4): n in [1..40]]; // Vincenzo Librandi, Dec 24 2013

CROSSREFS

Cf. A041798, A040399.

Sequence in context: A293290 A056972 A051391 * A187858 A072408 A318587

Adjacent sequences:  A041796 A041797 A041798 * A041800 A041801 A041802

KEYWORD

nonn,frac,easy

AUTHOR

N. J. A. Sloane.

EXTENSIONS

More terms from Colin Barker, Nov 25 2013

STATUS

approved

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Last modified February 20 15:52 EST 2020. Contains 332078 sequences. (Running on oeis4.)