OFFSET
1,1
COMMENTS
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..10000
Vincenzo Librandi, X^2-AY^2=1, Math Forum, 2007. [Wayback Machine link]
Index entries for linear recurrences with constant coefficients, signature (3,-3,1).
FORMULA
G.f.: 39*x*(-38-41*x+x^2)/(x-1)^3.
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3).
From Amiram Eldar, Mar 23 2023: (Start)
Sum_{n>=1} 1/a(n) = (1 - cot(Pi/sqrt(39))*Pi/sqrt(39))/78.
Sum_{n>=1} (-1)^(n+1)/a(n) = (cosec(Pi/sqrt(39))*Pi/sqrt(39) - 1)/78. (End)
MAPLE
MATHEMATICA
LinearRecurrence[{3, -3, 1}, {1482, 6045, 13650}, 50] (* Vincenzo Librandi, Feb 21 2012 *)
Table[1521n^2-39, {n, 30}] (* Harvey P. Dale, Aug 23 2019 *)
PROG
(Magma) I:=[1482, 6045, 13650]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+1*Self(n-3): n in [1..40]]; // Vincenzo Librandi, Feb 21 2012
(PARI) for(n=1, 40, print1(1521*n^2 - 39", ")); \\ Vincenzo Librandi, Feb 21 2012
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Mar 26 2009
EXTENSIONS
Comment rewritten and formula replaced by R. J. Mathar, Oct 22 2009
STATUS
approved