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 A209988 #8 Nov 27 2016 22:27:50
%S A209988 0,0,52,116,364,492,684,876,1260,1452,1836,2156,2668,3052,3628,3884,
%T A209988 4652,5164,5740,6316,7340,7724,8684,9388,10156,10796,11948,12524,
%U A209988 14060,14956,15724,16684,18220,18860,20396,21164,22700,23852,25580
%N A209988 Number of 2 X 2 matrices having all elements in {-n,...n} and determinant 4.
%C A209988 See A210000 for a guide to related sequences.
%H A209988 Chai Wah Wu, <a href="/A209988/b209988.txt">Table of n, a(n) for n = 0..10000</a>
%t A209988 (See the Mathematica section at A209981.)
%Y A209988 Cf. A210000.
%K A209988 nonn
%O A209988 0,3
%A A209988 _Clark Kimberling_, Mar 17 2012