OFFSET
0,1
COMMENTS
Smallest positive integer x satisfying the Pell equation x^2 - 3^(2*n-3) * y^2 = 1. - A.H.M. Smeets, Sep 29 2017
Term a(5) has 139 decimal digits and a(6) has 417 decimal digits. - Andrew Howroyd, Feb 25 2018
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..6
FORMULA
a(n) = cosh(3^n*arccosh(2)).
a(n) = ChebyshevT(3^n, 2). - Vladeta Jovovic, Jun 11 2004
From A.H.M. Smeets, Oct 02 2017: (Start)
a(n) = A001075(3^(n-2))
a(n) = A002350(3^(2n-3)). (End)
MATHEMATICA
NestList[4 #^3 - 3 # &, 2, 5] (* Michael De Vlieger, Oct 02 2017 *)
PROG
(PARI) a(n) = if (n==0, 2, 4*a(n-1)^3 - 3*a(n-1)); \\ Michel Marcus, Oct 03 2017
(PARI) a(n) = polchebyshev(3^n, 1, 2); \\ Michel Marcus, Oct 03 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Jose Eduardo Blazek, Jun 07 2004
EXTENSIONS
More terms from Vladeta Jovovic, Jun 11 2004
Offset corrected by Michel Marcus, Oct 03 2017
STATUS
approved