A042241 Denominators of continued fraction convergents to sqrt(646).

1, 2, 5, 12, 605, 1222, 3049, 7320, 369049, 745418, 1859885, 4465188, 225119285, 454703758, 1134526801, 2723757360, 137322394801, 277368546962, 692059488725, 1661487524412, 83766435709325, 169194358943062, 422155153595449, 1013504666133960, 51097388460293449

Offset

0,2

Links

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

Index entries for linear recurrences with constant coefficients, signature (0,0,0,610,0,0,0,-1).

Formula

G.f.: -(x^2 - 2*x - 1)*(x^4 + 6*x^2 + 1) / (x^8 - 610*x^4 + 1). - Colin Barker, Dec 05 2013

a(n) = 610*a(n-4) - a(n-8) for n > 7. - Vincenzo Librandi, Jan 18 2014

Mathematica

Denominator[Convergents[Sqrt[646], 30]] (* Vincenzo Librandi, Jan 18 2014 *)

Prog

(Magma) I:=[1, 2, 5, 12, 605, 1222, 3049, 7320]; [n le 8 select I[n] else 610*Self(n-4)-Self(n-8): n in [1..30]]; // Vincenzo Librandi, Jan 18 2014

Crossrefs

Cf. A042240, A040620.

Sequence in context: A041333 A197950 A041715 * A042911 A137918 A372875

Adjacent sequences: A042238 A042239 A042240 * A042242 A042243 A042244

Keyword

nonn,frac,easy

Author

N. J. A. Sloane

Extensions

More terms from Colin Barker, Dec 05 2013

Status

approved