OFFSET
0,1
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..200
Index entries for linear recurrences with constant coefficients, signature (0,40,0,-1).
FORMULA
G.f.: (19 + 20*x + 19*x^2 - x^3)/(1 - 40*x^2 + x^4). - Vincenzo Librandi, Nov 07 2013
a(n) = 40*a(n-2)-a(n-4). - Vincenzo Librandi, Nov 07 2013
MATHEMATICA
Numerator[Convergents[Sqrt[399], 30]] (* or *) CoefficientList[Series[(19 + 20 x + 19 x^2 - x^3)/(1 - 40 x^2 + x^4), {x, 0, 30}], x] (* Vincenzo Librandi, Nov 07 2013 *)
LinearRecurrence[{0, 40, 0, -1}, {19, 20, 779, 799}, 30] (* Harvey P. Dale, Sep 21 2018 *)
PROG
(Magma) I:=[19, 20, 779, 799]; [n le 4 select I[n] else 40*Self(n-2)-Self(n-4): n in [1..30]]; // Vincenzo Librandi, Nov 07 2013
CROSSREFS
KEYWORD
nonn,frac,easy
AUTHOR
STATUS
approved