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 A210001 #8 Nov 27 2016 21:20:05
%S A210001 0,0,1,7,11,23,39,59,71,115,127,163,199,243,263,339,367,427,471,539,
%T A210001 567,683,719,803,879,955,999,1139,1183,1291,1367,1483,1543,1739,1799,
%U A210001 1891,1983,2123,2191,2427,2487,2643,2759,2923,2999,3187,3271
%N A210001 Number of 2 X 2 matrices having all elements in {1,2,...,n} and determinant 3.
%C A210001 See A210000 for a guide to related sequences.
%H A210001 Chai Wah Wu, <a href="/A210001/b210001.txt">Table of n, a(n) for n = 0..10000</a>
%t A210001 (See the Mathematica section at A209978.)
%Y A210001 Cf. A210000, A209978.
%K A210001 nonn
%O A210001 0,4
%A A210001 _Clark Kimberling_, Mar 16 2012