OFFSET
0,1
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..200
Index entries for linear recurrences with constant coefficients, signature (0,42,0,-1).
FORMULA
G.f.: (20 + 21*x + 20*x^2 - x^3)/(1 - 42*x^2 + x^4). - Vincenzo Librandi, Nov 10 2013
a(n) = 42*a(n-2) - a(n-4). - Vincenzo Librandi, Nov 10 2013
MATHEMATICA
Numerator[Convergents[Sqrt[440], 30]] (* or *) CoefficientList[Series[(20 + 21 x + 20 x^2 - x^3)/(1 - 42 x^2 + x^4), {x, 0, 25}], x] (* Vincenzo Librandi, Nov 10 2013 *)
PROG
(Magma) I:=[20, 21, 860, 881]; [n le 8 select I[n] else 42*Self(n-2)-Self(n-4): n in [1..25]]; // Vincenzo Librandi, Nov 10 2013
CROSSREFS
KEYWORD
nonn,cofr,frac,easy,less
AUTHOR
STATUS
approved