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A154024
a(n+2) = 49*a(n+1) - a(n), a(1)=0, a(2)=7.
1
0, 7, 343, 16800, 822857, 40303193, 1974033600, 96687343207, 4735705783543, 231952896050400, 11360956200686057, 556454900937566393, 27254929189740067200, 1334935075396325726407
OFFSET
1,2
COMMENTS
If a(n)=x and a(n+1)=y, then (x^2+y^2)/(xy+1)=49.
FORMULA
G.f.: 7*x^2/(1 -49*x +x^2). - R. J. Mathar, Jan 05 2011
MATHEMATICA
LinearRecurrence[{49, -1}, {0, 7}, 30] (* Vincenzo Librandi, Feb 25 2012 *)
Rest@ CoefficientList[Series[7 x^2/(1 - 49 x + x^2), {x, 0, 14}], x] (* Michael De Vlieger, Sep 01 2016 *)
PROG
(PARI) concat(0, Vec(7/(1-49*x+x^2)+O(x^98))) \\ Charles R Greathouse IV, Dec 27 2011
(Magma) I:=[0, 7]; [n le 2 select I[n] else 49*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
STATUS
approved