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 A066406 #18 Dec 22 2024 20:02:32
%S A066406 0,24,192,1248,7680,46464,279552,1678848,10076160,60463104,362790912,
%T A066406 2176770048,13060669440,78364114944,470184886272,2821109710848,
%U A066406 16926659051520,101559955881984,609359738437632,3656158436917248,21936950634086400,131621703829684224
%N A066406 a(n) = 2^n*(3^n-3).
%C A066406 Number of orthogonal arrays OA(4,n,2,1).
%H A066406 Harry J. Smith, <a href="/A066406/b066406.txt">Table of n, a(n) for n = 1..150</a>
%H A066406 J.-Z. Zhang, Z.-S. You and Z.-L. Li, <a href="https://doi.org/10.1016/S0012-365X(01)00045-0">Enumeration of binary orthogonal arrays of strength 1</a>, Discrete Math., 239 (2000), 191-198.
%H A066406 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (8,-12).
%F A066406 From _Colin Barker_, Oct 20 2015: (Start)
%F A066406 a(n) = 8*a(n-1)-12*a(n-2).
%F A066406 G.f.: 24*x^2 / ((2*x-1)*(6*x-1)). (End)
%t A066406 Table[2^n(3^n-3),{n,30}] (* or *) LinearRecurrence[{8,-12},{0,24},30] (* _Harvey P. Dale_, Jul 28 2019 *)
%o A066406 (PARI) a(n) = { 2^n*(3^n - 3) } \\ _Harry J. Smith_, Feb 13 2010
%o A066406 (PARI) concat(0, Vec(24*x^2/((2*x-1)*(6*x-1)) + O(x^30))) \\ _Colin Barker_, Oct 20 2015
%K A066406 nonn,easy
%O A066406 1,2
%A A066406 _N. J. A. Sloane_, Dec 25 2001