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 A144720 #9 Jan 03 2024 23:43:22
%S A144720 2,3,10,37,138,515,1922,7173,26770,99907,372858,1391525,5193242,
%T A144720 19381443,72332530,269948677,1007462178,3759900035,14032137962,
%U A144720 52368651813,195442469290,729401225347,2722162432098,10159248503045
%N A144720 a(0) = 2, a(1) = 3, a(n) = 4 * a(n-1) - a(n-2).
%H A144720 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (4,-1).
%F A144720 Sequence satisfies -11 = f(a(n), a(n+1)) where f(u, v) = u^2 + v^2 - 4*u*v.
%F A144720 G.f.: (2 - 5*x) / (1 - 4*x + x^2). a(n) = (11 + a(n-1)^2) / a(n-2).
%t A144720 LinearRecurrence[{4,-1},{2,3},30] (* _Harvey P. Dale_, Aug 29 2015 *)
%o A144720 (PARI) {a(n) = real( (2 + quadgen(12))^n * ( 2 - 1 / quadgen(12) ))}
%o A144720 (PARI) {a(n) = subst( (4*polchebyshev(n) + polchebyshev(n-1)) / 3, x, 2)}
%Y A144720 Cf. A144721(n) = a(-n).
%K A144720 nonn
%O A144720 0,1
%A A144720 _Michael Somos_, Sep 19 2008