This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A094680 #43 Feb 25 2018 15:53:35 %S A094680 2,26,70226,1385331749802026, %T A094680 10634604778476758291777057017318241822792488226 %N A094680 a(n+1) = 4*a(n)^3 - 3*a(n), with a(0) = 2. %C A094680 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 A094680 Term a(5) has 139 decimal digits and a(6) has 417 decimal digits. - _Andrew Howroyd_, Feb 25 2018 %H A094680 Andrew Howroyd, <a href="/A094680/b094680.txt">Table of n, a(n) for n = 0..6</a> %F A094680 a(n) = cosh(3^n*arccosh(2)). %F A094680 a(n) = ChebyshevT(3^n, 2). - _Vladeta Jovovic_, Jun 11 2004 %F A094680 From _A.H.M. Smeets_, Oct 02 2017: (Start) %F A094680 a(n) = A001075(3^(n-2)) %F A094680 a(n) = A002350(3^(2n-3)). (End) %t A094680 NestList[4 #^3 - 3 # &, 2, 5] (* _Michael De Vlieger_, Oct 02 2017 *) %o A094680 (PARI) a(n) = if (n==0, 2, 4*a(n-1)^3 - 3*a(n-1)); \\ _Michel Marcus_, Oct 03 2017 %o A094680 (PARI) a(n) = polchebyshev(3^n, 1, 2); \\ _Michel Marcus_, Oct 03 2017 %Y A094680 Cf. A001075, A002812. %K A094680 nonn,easy %O A094680 0,1 %A A094680 _Jose Eduardo Blazek_, Jun 07 2004 %E A094680 More terms from _Vladeta Jovovic_, Jun 11 2004 %E A094680 Offset corrected by _Michel Marcus_, Oct 03 2017