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A041721 Denominators of continued fraction convergents to sqrt(380). 2
1, 2, 77, 156, 6005, 12166, 468313, 948792, 36522409, 73993610, 2848279589, 5770552788, 222129285533, 450029123854, 17323235991985, 35096501107824, 1350990278089297, 2737077057286418, 105359918454973181, 213456913967232780, 8216722649209818821 (list; graph; refs; listen; history; text; internal format)
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, 78, 0, -1).

FORMULA

G.f.: -(x^2-2*x-1) / (x^4-78*x^2+1). - Colin Barker, Nov 22 2013

a(n) = 78*a(n-2) - a(n-4) for n>3. - Vincenzo Librandi, Dec 23 2013

MAPLE

convert(sqrt(380), confrac, 30, cvgts): denom(cvgts); # Wesley Ivan Hurt, Dec 23 2013

MATHEMATICA

Denominator[Convergents[Sqrt[380], 30]] (* Harvey P. Dale, May 29 2013 *)

CoefficientList[Series[(1 + 2 x - x^2)/(x^4 - 78 x^2 + 1), {x, 0, 30}], x] (* Vincenzo Librandi, Dec 23 2013 *)

PROG

(MAGMA) I:=[1, 2, 77, 156]; [n le 4 select I[n] else 78*Self(n-2)-Self(n-4): n in [1..40]]; // Vincenzo Librandi, Dec 23 2013

CROSSREFS

Cf. A041720, A040360.

Sequence in context: A087287 A266877 A301472 * A048358 A124456 A338588

Adjacent sequences:  A041718 A041719 A041720 * A041722 A041723 A041724

KEYWORD

nonn,frac,easy

AUTHOR

N. J. A. Sloane.

EXTENSIONS

More terms from Colin Barker, Nov 22 2013

STATUS

approved

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Last modified September 20 14:44 EDT 2021. Contains 347586 sequences. (Running on oeis4.)