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 A152056 #13 Jun 29 2023 23:55:10
%S A152056 1,9,84,810,8028,81324,837648,8734392,91882512,972602640,10340011584,
%T A152056 110257202592,1178108743104,12605895573696,135013638364416,
%U A152056 1446985635811200,15514677652177152,166399318145915136
%N A152056 a(n) = ((9+sqrt(3))^n + (9-sqrt(3))^n)/2.
%H A152056 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (18, -78).
%F A152056 From _Philippe Deléham_, Nov 26 2008: (Start)
%F A152056 a(n) = 18*a(n-1) - 78*a(n-2), n > 1; a(0)=1, a(1)=9.
%F A152056 G.f.: (1-9*x)/(1-18*x+78*x^2).
%F A152056 a(n) = (Sum_{k=0..n} A098158(n,k)*3^(3*k))/3^n. (End)
%o A152056 (Magma) Z<x>:= PolynomialRing(Integers()); N<r3>:=NumberField(x^2-3); S:=[ ((9+r3)^n+(9-r3)^n)/2: n in [0..19] ]; [ Integers()!S[j]: j in [1..#S] ]; // _Klaus Brockhaus_, Nov 26 2008
%K A152056 nonn
%O A152056 0,2
%A A152056 Al Hakanson (hawkuu(AT)gmail.com), Nov 22 2008
%E A152056 Extended beyond a(6) by _Klaus Brockhaus_, Nov 26 2008