A042219 Denominators of continued fraction convergents to sqrt(635).

1, 5, 251, 1260, 63251, 317515, 15939001, 80012520, 4016565001, 20162837525, 1012158441251, 5080955043780, 255059910630251, 1280380508195035, 64274085320382001, 322650807110105040, 16196814440825634001, 81306723011238275045, 4081532965002739386251

Offset

0,2

Links

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

Index entries for linear recurrences with constant coefficients, signature (0,252,0,-1).

Formula

G.f.: -(x^2 - 5*x - 1) / (x^4 - 252*x^2 + 1). - Colin Barker, Dec 04 2013

a(n) = 252*a(n-2) - a(n-4) for n > 3. - Vincenzo Librandi, Jan 17 2014

Mathematica

Denominator[Convergents[Sqrt[635], 30]] (* Vincenzo Librandi, Jan 17 2014 *)

Prog

(Magma) I:=[1, 5, 251, 1260]; [n le 4 select I[n] else 252*Self(n-2)-Self(n-4): n in [1..30]]; // Vincenzo Librandi, Jan 17 2014

Crossrefs

Cf. A042218, A040609.

Sequence in context: A282734 A115739 A142202 * A198600 A213446 A276485

Adjacent sequences: A042216 A042217 A042218 * A042220 A042221 A042222

Keyword

nonn,frac,easy

Author

N. J. A. Sloane

Extensions

More terms from Colin Barker, Dec 04 2013

Status

approved