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A211143 Number of 2 X 2 matrices having all terms in {-n, ..., 0, ..., n} and determinant = n^2.

%I A211143 #11 Jul 23 2017 21:56:14
%S A211143 1,20,52,84,132,156,260,228,356,372,492,404,804,508,820,844,964,716,
%T A211143 1396,852,1660,1380,1540,1092,2452,1476,1932,1876,2564,1532,3884,1700,
%U A211143 3012,2676,3004,2876,4916,2172,3684,3484,5260
%N A211143 Number of 2 X 2 matrices having all terms in {-n, ..., 0, ..., n} and determinant = n^2.
%C A211143 For a guide to related sequences, see A210000.
%H A211143 Chai Wah Wu, <a href="/A211143/b211143.txt">Table of n, a(n) for n = 0..3000</a>
%t A211143 a = -n; b = n; z1 = 40;
%t A211143 t[n_] := t[n] = Flatten[Table[w*z - x*y, {w, a, b}, {x, a, b}, {y, a, b}, {z, a, b}]]
%t A211143 c[n_, k_] := c[n, k] = Count[t[n], k]
%t A211143 Table[c[n, n^2], {n, 0, z1}]         (* A211143 *)
%t A211143 (1/4) Table[c[n, n^2], {n, 1, z1}]   (* integers *)
%Y A211143 Cf. A210000.
%K A211143 nonn
%O A211143 0,2
%A A211143 _Clark Kimberling_, Apr 03 2012