OFFSET
0,1
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..200
Index entries for linear recurrences with constant coefficients, signature (0,0,0,610,0,0,0,-1).
FORMULA
G.f.: (1 +x)*(25 +26*x +101*x^2 +204*x^3 -77*x^4 +26*x^5 -x^6)/(1 -610*x^4 +x^8) = (25 +51*x +127*x^2 +305*x^3 +127*x^4 -51*x^5 +25*x^6 -x^7)/(1 -610*x^4 +x^8). - Vincenzo Librandi, Nov 19 2013
a(n) = 610*a(n-4) - a(n-8). - Vincenzo Librandi, Nov 19 2013
MATHEMATICA
Numerator[Convergents[Sqrt[646], 30]] (* or *) CoefficientList[Series[(25 + 51 x + 127 x^2 + 305 x^3 + 127 x^4 - 51 x^5 + 25 x^6 - x^7)/(1 - 610 x^4 + x^8), {x, 0, 20}], x] (* Vincenzo Librandi, Nov 19 2013 *)
PROG
(Magma) I:=[25, 51, 127, 305, 15377, 31059, 77495, 186049]; [n le 8 select I[n] else 610*Self(n-4)-Self(n-8): n in [1..30]]; // Vincenzo Librandi, Nov 19 2013
CROSSREFS
KEYWORD
nonn,cofr,frac,easy
AUTHOR
STATUS
approved