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 A275155 #46 Sep 08 2022 08:46:17
%S A275155 18,64,338,1936,11250,65536,381938,2226064,12974418,75620416,
%T A275155 440748050,2568867856,14972459058,87265886464,508622859698,
%U A275155 2964471271696,17278204770450,100704757350976,586950339335378,3420997278661264,19939033332632178,116213202717131776
%N A275155 a(1) = 18; a(n) = 3*a(n - 1) + 2*sqrt(2*a(n - 1)*(a(n - 1) - 14)) - 14 for n > 1.
%H A275155 Colin Barker, <a href="/A275155/b275155.txt">Table of n, a(n) for n = 1..1000</a>
%H A275155 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (7,-7,1).
%F A275155 a(n+1) = 3*a(n) + 2*sqrt(2*a(n)*(a(n) - 14)) - 14.
%F A275155 From _Colin Barker_, Jul 21 2016: (Start)
%F A275155 a(n) = (14+(9-4*sqrt(2))*(3+2*sqrt(2))^n + (3-2*sqrt(2))^n*(9+4*sqrt(2)))/2.
%F A275155 a(n) = 7*a(n-1) -7*a(n-2) +a(n-3) for n>3.
%F A275155 G.f.: 2*x*(9-31*x+8*x^2) / ((1-x)*(1-6*x+x^2)). (End)
%t A275155 NestList[3 # + 2 Sqrt[2 # (# - 14)] - 14 &, 18, 18] (* _Michael De Vlieger_, Jul 19 2016 *)
%t A275155 CoefficientList[Series[2*x*(9-31*x+8*x^2)/((1-x)*(1-6*x+x^2)), {x, 0, 50}], x] (* _G. C. Greubel_, Sep 30 2018 *)
%o A275155 (PARI) a(n)=([0,1,0; 0,0,1; 1,-7,7]^(n-1)*[18;64;338])[1,1] \\ _Charles R Greathouse IV_, Jul 20 2016
%o A275155 (PARI) Vec(2*x*(9-31*x+8*x^2)/((1-x)*(1-6*x+x^2)) + O(x^30)) \\ _Colin Barker_, Jul 21 2016
%o A275155 (Magma) m:=30; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!(2*x*(9-31*x+8*x^2)/((1-x)*(1-6*x+x^2)))); // _G. C. Greubel_, Sep 30 2018
%K A275155 nonn,easy
%O A275155 1,1
%A A275155 _Manuel López Holgueras_, Jul 18 2016