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 A209984 #8 Nov 27 2016 21:19:46
%S A209984 0,4,92,156,284,412,604,796,1052,1244,1628,1948,2204,2588,3164,3420,
%T A209984 3932,4444,5020,5596,6108,6492,7452,8156,8668,9308,10460,11036,11804,
%U A209984 12700,13468,14428,15452,16092,17628,18396,19164,20316,22044
%N A209984 Number of 2 X 2 matrices having all elements in {-n,...n} and determinant 2.
%C A209984 See A210000 for a guide to related sequences.
%H A209984 Chai Wah Wu, <a href="/A209984/b209984.txt">Table of n, a(n) for n = 0..10000</a>
%e A209984 a(1) counts these matrices (in reduced notation):
%e A209984 (-1,-1,1,-1), (-1,1,-1,-1), (1,-1,1,1), (1,1,-1,1)
%t A209984 (See the Mathematica section at A209981.)
%Y A209984 Cf. A210000.
%K A209984 nonn
%O A209984 0,2
%A A209984 _Clark Kimberling_, Mar 17 2012