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A042181
Denominators of continued fraction convergents to sqrt(615).
2
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
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
Sequence in context: A041745 A298224 A051152 * A368531 A042717 A304286
KEYWORD
nonn,frac,easy
EXTENSIONS
More terms from Colin Barker, Dec 03 2013
STATUS
approved