OFFSET
1,2
COMMENTS
If a(n)=x and a(n+1)=y then (x^2+y^2)/(xy+1)=81.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..200
Index entries for linear recurrences with constant coefficients, signature (81,-1).
FORMULA
G.f.: (9*x)/(1 -81*x +x^2). - Harvey P. Dale, Sep 15 2011
MATHEMATICA
LinearRecurrence[{81, -1}, {0, 9}, 20] (* Harvey P. Dale, Sep 15 2011 *)
PROG
(PARI) concat(0, Vec(9/(x^2-81*x+1)+O(x^98))) \\ Charles R Greathouse IV, Dec 27 2011
(Magma) I:=[0, 9]; [n le 2 select I[n] else 81*Self(n-1)-Self(n-2): n in [1..50]]; // Vincenzo Librandi, Feb 25 2012
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Jan 04 2009
EXTENSIONS
More terms from Harvey P. Dale, Sep 15 2011
STATUS
approved