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 A238777 #30 Feb 16 2025 08:33:21
%S A238777 1,1,2,3,6,10,17,29,49,82,137,229,382,638,1063,1772,2953,4923,8205,
%T A238777 13675,22792,37987,63312,105521,175868,293114,488524,814207,1357012,
%U A238777 2261686,3769478,6282463,10470772,17451288,29085480
%N A238777 a(n) = floor((5^n+1)/(2*3^n)).
%C A238777 a(n) is the rounded-down perimeter of the Vicsek fractal after n iterations. The Vicsek fractal is a subset of the box fractal; for both types, the number of boxes = A000351(n). See illustrations in links.
%H A238777 Vincenzo Librandi, <a href="/A238777/b238777.txt">Table of n, a(n) for n = 1..1000</a>
%H A238777 Kival Ngaokrajang, <a href="/A238777/a238777_1.pdf">Illustrations of initial terms</a>
%H A238777 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/BoxFractal.html">Box Fractal</a>
%H A238777 Wikipedia, <a href="http://en.wikipedia.org/wiki/Vicsek_fractal">Vicsek Fractal</a>
%F A238777 a(n) = A034478(n)/3^n.
%p A238777 A238777:=n->floor((5^n+1)/(2*3^n)); seq(A238777(n), n=1..50); # _Wesley Ivan Hurt_, Mar 09 2014
%t A238777 Table[Floor[(5^n + 1)/(2*3^n)], {n, 50}] (* _Wesley Ivan Hurt_, Mar 09 2014 *)
%o A238777 (Small Basic)
%o A238777 For n = 1 to 40
%o A238777 x = (math.Power(5,n)+1)/(2*math.Power(3,n))
%o A238777 a = math.Floor(x)
%o A238777 TextWindow.Write(a+", ")
%o A238777 Endfor
%o A238777 (PARI)
%o A238777 vector(100, n, floor((5^n+1)/(2*3^n))) \\ _Colin Barker_, Mar 05 2014
%o A238777 (Magma) [Floor((5^n+1)/(2*3^n)): n in [1..40]]; // _Vincenzo Librandi_, Mar 11 2014
%Y A238777 Cf. A000351, A034478.
%K A238777 nonn
%O A238777 1,3
%A A238777 _Kival Ngaokrajang_, Mar 05 2014