A042181 Denominators of continued fraction convergents to sqrt(615).

1, 1, 4, 5, 244, 249, 991, 1240, 60511, 61751, 245764, 307515, 15006484, 15313999, 60948481, 76262480, 3721547521, 3797810001, 15114977524, 18912787525, 922928778724, 941841566249, 3748453477471, 4690295043720, 228882615576031, 233572910619751

Offset

0,3

Links

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

Index entries for linear recurrences with constant coefficients, signature (0,0,0,248,0,0,0,-1).

Formula

G.f.: -(x^2 - x - 1)*(x^4 + 5*x^2 + 1) / (x^8 - 248*x^4 + 1). - Colin Barker, Dec 03 2013

a(n) = 248*a(n-4) - a(n-8) for n > 7. - Vincenzo Librandi, Jan 16 2014

Mathematica

Denominator[Convergents[Sqrt[615], 30]] (* Vincenzo Librandi, Jan 16 2014 *)

Prog

(Magma) I:=[1, 1, 4, 5, 244, 249, 991, 1240]; [n le 8 select I[n] else 248*Self(n-4)-Self(n-8): n in [1..30]]; // Vincenzo Librandi, Jan 16 2014

Crossrefs

Cf. A042180, A040590.

Sequence in context: A041745 A298224 A051152 * A368531 A042717 A304286

Adjacent sequences: A042178 A042179 A042180 * A042182 A042183 A042184

Keyword

nonn,frac,easy

Author

N. J. A. Sloane

Extensions

More terms from Colin Barker, Dec 03 2013

Status

approved