A041799 Denominators of continued fraction convergents to sqrt(420).

1, 2, 81, 164, 6641, 13446, 544481, 1102408, 44640801, 90384010, 3660001201, 7410386412, 300075457681, 607561301774, 24602527528641, 49812616359056, 2017107181890881, 4084026980140818, 165378186387523601, 334840399755188020, 13558994176595044401

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 A371508 A352742

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