OFFSET
1,1
COMMENTS
The identity (200*n-1)^2-(100*n^2-n)*(20)^2=1 can be written as a(n)^2-A157659(n)*(20)^2=1.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..10000
Vincenzo Librandi, X^2-AY^2=1
E. J. Barbeau, Polynomial Excursions, Chapter 10: Diophantine equations (2010), pages 84-85 (row 14 in the first table at p. 85, case d(t) = t*(10^2*t-1)).
Index entries for linear recurrences with constant coefficients, signature (2,-1).
FORMULA
a(n) = 2*a(n-1)-a(n-2).
G.f.: x*(199+x)/(1-x)^2.
MATHEMATICA
LinearRecurrence[{2, -1}, {199, 399}, 50]
PROG
(Magma) I:=[199, 399]; [n le 2 select I[n] else 2*Self(n-1)-Self(n-2): n in [1..50]];
(PARI) a(n) = 200*n - 1.
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Mar 10 2009
STATUS
approved