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 A168493 #15 Sep 08 2022 08:45:49
%S A168493 1,1,9,81,6561,531441,387420489,282429536481,1853020188851841,
%T A168493 12157665459056928801,717897987691852588770249,
%U A168493 42391158275216203514294433201,22528399544939174411840147874772641,11972515182562019788602740026717047105681
%N A168493 a(n) = 3^floor(n^2/2).
%C A168493 Hankel transform of A168492. A trivial Somos-4 sequence linked to elliptic curve y^2 = 1 - 16x + 76x^2 - 96x^3.
%H A168493 G. C. Greubel, <a href="/A168493/b168493.txt">Table of n, a(n) for n = 0..50</a>
%F A168493 a(n) = 3^floor(n^2/2) = 9^floor(n^2/4) = 9^A002620(n) = 81*a(n-2)^2/a(n-4).
%t A168493 Table[3^Floor[n^2/2],{n,0,20}] (* _Harvey P. Dale_, Mar 06 2011 *)
%o A168493 (Magma) [3^Floor(n^2/2): n in [0..15]]; // _Vincenzo Librandi_, Jul 24 2016
%K A168493 easy,nonn
%O A168493 0,3
%A A168493 _Paul Barry_, Nov 27 2009