OFFSET
0,2
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..200
Index entries for linear recurrences with constant coefficients, signature (0, 90, 0, -1).
FORMULA
G.f.: -(x^2 -2*x -1) / (x^4 -90*x^2 +1). - Colin Barker, Nov 28 2013
a(n) = 90*a(n-2) - a(n-4) for n>3. - Vincenzo Librandi, Dec 28 2013
MATHEMATICA
Denominator[Convergents[Sqrt[506], 30]] (* Vincenzo Librandi, Dec 28 2013 *)
LinearRecurrence[{0, 90, 0, -1}, {1, 2, 89, 180}, 40] (* Harvey P. Dale, Jan 21 2016 *)
PROG
(Magma) I:=[1, 2, 89, 180]; [n le 4 select I[n] else 90*Self(n-2)-Self(n-4): n in [1..40]]; // Vincenzo Librandi, Dec 28 2013
CROSSREFS
KEYWORD
nonn,frac,easy
AUTHOR
EXTENSIONS
More terms from Colin Barker, Nov 28 2013
STATUS
approved