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A042241
Denominators of continued fraction convergents to sqrt(646).
2
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
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
Sequence in context: A041333 A197950 A041715 * A042911 A137918 A372875
KEYWORD
nonn,frac,easy
EXTENSIONS
More terms from Colin Barker, Dec 05 2013
STATUS
approved