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 A211055 #10 Jan 11 2017 01:32:17
%S A211055 0,1,4,9,20,23,51,55,88,79,181,121,214,222,323,227,484,299,605,488,
%T A211055 604,457,1102,623,902,876,1269,769,1754,893,1728,1370,1634,1436,2811,
%U A211055 1303,2100,1964,3184,1637,3622,1823,3403,3171,3138
%N A211055 Number of 2 X 2 matrices having all terms in {1,...,n} and determinant n+1.
%C A211055 For a guide to related sequences, see A210000.
%H A211055 Chai Wah Wu, <a href="/A211055/b211055.txt">Table of n, a(n) for n = 1..3000</a>
%t A211055 a = 1; b = n; z1 = 45;
%t A211055 t[n_] := t[n] = Flatten[Table[w*z - x*y, {w, a, b}, {x, a, b}, {y, a, b}, {z, a, b}]]
%t A211055 c[n_, k_] := c[n, k] = Count[t[n], k]
%t A211055 Table[c[n, n + 1], {n, 1, z1}] (* A211055 *)
%Y A211055 Cf. A210000, A211053.
%K A211055 nonn
%O A211055 1,3
%A A211055 _Clark Kimberling_, Mar 31 2012