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 A241038 #16 Feb 09 2024 12:38:57
%S A241038 0,1,28,325,3160,29161,264628,2388205,21513520,193680721,1743303628,
%T A241038 15690264085,141213971080,1270930522681,11438389053028,
%U A241038 102945544523965,926510029855840,8338590656123041,75047317067368828
%N A241038 a(n) = A000217(A058481(n)).
%C A241038 a(n) is the total number of hexagon holes in triflake-like fractal (A240917) after n iterations. A240917(n) - a(n) is the total number of rhombic holes.
%H A241038 Kival Ngaokrajang, <a href="/A241038/a241038.pdf">Illustration of initial terms</a>
%H A241038 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (13,-39,27).
%F A241038 a(n) = (1/2)*3^(2*n) - (3/2)*3^n + 1.
%F A241038 a(n) = 13*a(n-1)-39*a(n-2)+27*a(n-3). G.f.: -x*(15*x+1) / ((x-1)*(3*x-1)*(9*x-1)). - _Colin Barker_, Apr 15 2014
%p A241038 A241038:=n->(1/2)*3^(2*n) - (3/2)*3^n + 1; seq(A241038(n), n=0..30); # _Wesley Ivan Hurt_, Apr 15 2014
%t A241038 Table[(1/2)*3^(2 n) - (3/2)*3^n + 1, {n, 0, 30}] (* _Wesley Ivan Hurt_, Apr 15 2014 *)
%t A241038 LinearRecurrence[{13,-39,27},{0,1,28},30] (* _Harvey P. Dale_, Oct 12 2017 *)
%o A241038 (PARI) a(n)= (1/2)*3^(2*n) - (3/2)*3^n + 1
%o A241038 for(n=0,100,print1(a(n),", "))
%o A241038 (PARI) Vec(-x*(15*x+1)/((x-1)*(3*x-1)*(9*x-1)) + O(x^100)) \\ _Colin Barker_, Apr 15 2014
%Y A241038 Cf. A000217, A058481, A240917.
%K A241038 nonn,easy
%O A241038 0,3
%A A241038 _Kival Ngaokrajang_, Apr 15 2014