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 A287120 #23 Dec 02 2017 02:20:29
%S A287120 1,8,25,70,225,748,2401,7668,24649,79344,255025,819494,2634129,
%T A287120 8467464,27217089,87483296,281199361,903867144,2905317801,9338615022,
%U A287120 30017295025,96485195716,310134268609,996870677460,3204261102025,10299519778080,33105949765729,106413107836334
%N A287120 Number of non-attacking bishop positions on a 3 X n chessboard.
%H A287120 Colin Barker, <a href="/A287120/b287120.txt">Table of n, a(n) for n = 0..1000</a>
%H A287120 Richard M. Low and Ardak Kapbasov, <a href="https://www.emis.de/journals/JIS/VOL20/Low/low2.html">Non-Attacking Bishop and King Positions on Regular and Cylindrical Chessboards</a>, Journal of Integer Sequences, Vol. 20 (2017), Article 17.6.1, Table 1.
%H A287120 <a href="/index/Rec#order_09">Index entries for linear recurrences with constant coefficients</a>, signature (3,0,2,4,-10,-2,0,-1,1).
%F A287120 G.f.: (-1-5*x-x^2+7*x^3+5*x^4-x^5+x^6-x^7) / (-1+3*x +2*x^3 +4*x^4 -10*x^5 -2*x^6 -x^8 +x^9).
%t A287120 CoefficientList[Series[(-1 - 5 x - x^2 + 7 x^3 + 5 x^4 - x^5 + x^6 - x^7)/(-1 + 3 x + 2 x^3 + 4 x^4 - 10 x^5 - 2 x^6 - x^8 + x^9), {x, 0, 27}], x] (* _Michael De Vlieger_, May 20 2017 *)
%o A287120 (PARI) Vec((-1-5*x-x^2+7*x^3+5*x^4-x^5+x^6-x^7)/ (-1+3*x+2*x^3 +4*x^4-10*x^5-2*x^6-x^8+x^9) + O(x^30)) \\ _Michel Marcus_, May 20 2017
%Y A287120 Cf. A287168, A287169.
%K A287120 nonn,easy
%O A287120 0,2
%A A287120 _Richard M. Low_, May 20 2017