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A154026
a(n+2) = 81*a(n+1) - a(n), a(1)=0, a(2)=9.
2
0, 9, 729, 59040, 4781511, 387243351, 31361929920, 2539929080169, 205702893563769, 16659394449585120, 1349205247522830951, 109268965654899721911, 8849437012799354643840, 716695129071092826429129, 58043456017745719586115609, 4700803242308332193648935200
OFFSET
1,2
COMMENTS
If a(n)=x and a(n+1)=y then (x^2+y^2)/(xy+1)=81.
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