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 A209986 #8 Nov 27 2016 22:27:45
%S A209986 0,0,24,176,240,368,528,720,848,1232,1360,1680,2000,2384,2576,3216,
%T A209986 3472,3984,4368,4944,5200,6160,6480,7184,7824,8464,8848,10000,10384,
%U A209986 11280,11920,12880,13392,14992,15504,16272,17040,18192,18768,20688
%N A209986 Number of 2 X 2 matrices having all elements in {-n,...n} and determinant 3.
%C A209986 See A210000 for a guide to related sequences.
%H A209986 Chai Wah Wu, <a href="/A209986/b209986.txt">Table of n, a(n) for n = 0..10000</a>
%t A209986 (See the Mathematica section at A209981.)
%Y A209986 Cf. A210000.
%K A209986 nonn
%O A209986 0,3
%A A209986 _Clark Kimberling_, Mar 17 2012