A041767 Denominators of continued fraction convergents to sqrt(404).

1, 10, 401, 4020, 161201, 1616030, 64802401, 649640040, 26050404001, 261153680050, 10472197606001, 104983129740060, 4209797387208401, 42202957001824070, 1692328077460171201, 16965483731603536080, 680311677341601614401, 6820082257147619680090

Offset

0,2

Links

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

Index entries for linear recurrences with constant coefficients, signature (0,402,0,-1).

Formula

G.f.: -(x^2-10*x-1) / ((x^2-20*x-1)*(x^2+20*x-1)). - Colin Barker, Nov 24 2013

a(n) = 402*a(n-2) - a(n-4) for n>3. - Vincenzo Librandi, Dec 24 2013

Mathematica

Denominator[Convergents[Sqrt[404], 30]] (* Vincenzo Librandi, Dec 24 2013 *)

Prog

(Magma) I:=[1, 10, 401, 4020]; [n le 4 select I[n] else 402*Self(n-2)-Self(n-4): n in [1..40]]; // Vincenzo Librandi, Dec 24 2013

Crossrefs

Cf. A041766, A040383.

Sequence in context: A172505 A098722 A162677 * A130557 A231052 A364118

Adjacent sequences: A041764 A041765 A041766 * A041768 A041769 A041770

Keyword

nonn,frac,easy

Author

N. J. A. Sloane.

Extensions

More terms from Colin Barker, Nov 24 2013

Status

approved