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%I #43 Feb 25 2018 15:53:35
%S 2,26,70226,1385331749802026,
%T 10634604778476758291777057017318241822792488226
%N a(n+1) = 4*a(n)^3 - 3*a(n), with a(0) = 2.
%C Smallest positive integer x satisfying the Pell equation x^2 - 3^(2*n-3) * y^2 = 1. - _A.H.M. Smeets_, Sep 29 2017
%C Term a(5) has 139 decimal digits and a(6) has 417 decimal digits. - _Andrew Howroyd_, Feb 25 2018
%H Andrew Howroyd, <a href="/A094680/b094680.txt">Table of n, a(n) for n = 0..6</a>
%F a(n) = cosh(3^n*arccosh(2)).
%F a(n) = ChebyshevT(3^n, 2). - _Vladeta Jovovic_, Jun 11 2004
%F From _A.H.M. Smeets_, Oct 02 2017: (Start)
%F a(n) = A001075(3^(n-2))
%F a(n) = A002350(3^(2n-3)). (End)
%t NestList[4 #^3 - 3 # &, 2, 5] (* _Michael De Vlieger_, Oct 02 2017 *)
%o (PARI) a(n) = if (n==0, 2, 4*a(n-1)^3 - 3*a(n-1)); \\ _Michel Marcus_, Oct 03 2017
%o (PARI) a(n) = polchebyshev(3^n, 1, 2); \\ _Michel Marcus_, Oct 03 2017
%Y Cf. A001075, A002812.
%K nonn,easy
%O 0,1
%A _Jose Eduardo Blazek_, Jun 07 2004
%E More terms from _Vladeta Jovovic_, Jun 11 2004
%E Offset corrected by _Michel Marcus_, Oct 03 2017
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