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 A209992 #6 Jan 12 2017 01:37:01
%S A209992 0,1,8,23,46,77,120,167,230,301,384,463,590,685,808,959,1118,1245,
%T A209992 1448,1591,1830,2053,2256,2431,2766,3005,3248,3535,3886,4109,4560,
%U A209992 4799,5182,5549,5872,6295,6870,7157,7520,7959,8582
%N A209992 Number of 2 X 2 matrices with all elements in {1,2,...,n} and determinant in {0,1}.
%C A209992 See A210000 for a guide to related sequences.
%t A209992 a = 1; b = n; z1 = 40;
%t A209992 t[n_] := t[n] = Flatten[Table[w*z - x*y, {w, a, b}, {x, a, b}, {y, a, b}, {z, a, b}]]
%t A209992 c[n_, k_] := c[n, k] = Count[t[n], k]
%t A209992 c1[n_, m_] := c1[n, m] = Sum[c[n, k], {k, 0, 1}]
%t A209992 Table[c1[n, 1], {n, 0, z1}] (* A209992 *)
%Y A209992 Cf. A210000.
%K A209992 nonn
%O A209992 0,3
%A A209992 _Clark Kimberling_, Mar 18 2012