OFFSET
0,1
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..200
Index entries for linear recurrences with constant coefficients, signature (0,402,0,-1).
FORMULA
G.f.: (20 + 201*x + 20*x^2 - x^3)/(1 - 402*x^2 + x^4). - Vincenzo Librandi, Nov 07 2013
a(n) = 402*a(n-2)-a(n-4). - Vincenzo Librandi, Nov 07 2013
MATHEMATICA
Numerator[Convergents[Sqrt[404], 30]] (* or *) CoefficientList[Series[(20 + 201 x + 20 x^2 - x^3)/(1 - 402 x^2 + x^4), {x, 0, 30}], x] (* Vincenzo Librandi, Nov 07 2013 *)
LinearRecurrence[{0, 402, 0, -1}, {20, 201, 8060, 80801}, 20] (* Harvey P. Dale, Oct 27 2018 *)
PROG
(Magma) I:=[20, 201, 8060, 80801]; [n le 4 select I[n] else 402*Self(n-2)-Self(n-4): n in [1..30]]; // Vincenzo Librandi, Nov 07 2013
CROSSREFS
KEYWORD
nonn,frac,easy,less
AUTHOR
STATUS
approved