A041799 - OEIS

%I #19 Sep 08 2022 08:44:54

%S 1,2,81,164,6641,13446,544481,1102408,44640801,90384010,3660001201,

%T 7410386412,300075457681,607561301774,24602527528641,49812616359056,

%U 2017107181890881,4084026980140818,165378186387523601,334840399755188020,13558994176595044401

%N Denominators of continued fraction convergents to sqrt(420).

%H Vincenzo Librandi, <a href="/A041799/b041799.txt">Table of n, a(n) for n = 0..200</a>

%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,82,0,-1).

%F G.f.: -(x^2-2*x-1) / (x^4-82*x^2+1). - _Colin Barker_, Nov 25 2013

%F a(n) = 82*a(n-2) - a(n-4) for n>3. - _Vincenzo Librandi_, Dec 24 2013

%t Denominator[Convergents[Sqrt[420], 30]] (* _Vincenzo Librandi_, Dec 24 2013 *)

%o (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

%Y Cf. A041798, A040399.

%K nonn,frac,easy

%O 0,2

%A _N. J. A. Sloane_.

%E More terms from _Colin Barker_, Nov 25 2013