login
A042917
Denominators of continued fraction convergents to sqrt(990).
2
1, 2, 13, 28, 1749, 3526, 22905, 49336, 3081737, 6212810, 40358597, 86930004, 5430018845, 10946967694, 71111825009, 153170617712, 9567690123153, 19288550864018, 125298995307261, 269886541478540, 16858264566976741, 33986415675432022, 220776758619568873
OFFSET
0,2
FORMULA
G.f.: -(x^2-2*x-1)*(x^4+14*x^2+1) / ((x^4-42*x^2+1)*(x^4+42*x^2+1)). - Colin Barker, Dec 25 2013
a(n) = 1762*a(n-4) - a(n-8) for n>7. - Vincenzo Librandi, Feb 01 2014
MATHEMATICA
Denominator[Convergents[Sqrt[990], 30]] (* Vincenzo Librandi, Feb 01 2014 *)
PROG
(Magma) I:=[1, 2, 13, 28, 1749, 3526, 22905, 49336]; [n le 8 select I[n] else 1762*Self(n-4)-Self(n-8): n in [1..30]]; // Vincenzo Librandi, Feb 01 2014
CROSSREFS
Sequence in context: A041017 A033837 A041575 * A366720 A174049 A141336
KEYWORD
nonn,frac,easy
EXTENSIONS
More terms from Colin Barker, Dec 25 2013
STATUS
approved