OFFSET
0,1
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..200
Index entries for linear recurrences with constant coefficients, signature (0,128,0,-1).
FORMULA
G.f.: -(x^3-21*x^2-64*x-21)/(x^4-128*x^2+1). - Vincenzo Librandi, Nov 11 2013
a(n) = 128*a(n-2)-a(n-4). - Vincenzo Librandi, Nov 11 2013
MATHEMATICA
Numerator[Convergents[Sqrt[455], 30]] (* or *) CoefficientList[Series[-(x^3 - 21 x^2 - 64 x - 21)/(x^4 - 128 x^2 + 1), {x, 0, 25}], x] (* Vincenzo Librandi, Nov 11 2013 *)
PROG
(Magma) I:=[21, 64, 2709, 8191]; [n le 4 select I[n] else 128*Self(n-2)-Self(n-4): n in [1..20]]; // Vincenzo Librandi, Nov 11 2013
CROSSREFS
KEYWORD
nonn,cofr,frac,easy,less
AUTHOR
STATUS
approved