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A041767
Denominators of continued fraction convergents to sqrt(404).
2
1, 10, 401, 4020, 161201, 1616030, 64802401, 649640040, 26050404001, 261153680050, 10472197606001, 104983129740060, 4209797387208401, 42202957001824070, 1692328077460171201, 16965483731603536080, 680311677341601614401, 6820082257147619680090
OFFSET
0,2
FORMULA
G.f.: -(x^2-10*x-1) / ((x^2-20*x-1)*(x^2+20*x-1)). - Colin Barker, Nov 24 2013
a(n) = 402*a(n-2) - a(n-4) for n>3. - Vincenzo Librandi, Dec 24 2013
MATHEMATICA
Denominator[Convergents[Sqrt[404], 30]] (* Vincenzo Librandi, Dec 24 2013 *)
PROG
(Magma) I:=[1, 10, 401, 4020]; [n le 4 select I[n] else 402*Self(n-2)-Self(n-4): n in [1..40]]; // Vincenzo Librandi, Dec 24 2013
CROSSREFS
Sequence in context: A172505 A098722 A162677 * A130557 A231052 A364118
KEYWORD
nonn,frac,easy
AUTHOR
EXTENSIONS
More terms from Colin Barker, Nov 24 2013
STATUS
approved