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A211156 Number of 2 X 2 matrices having all terms in {-n,...,0,..,n} and even nonnegative determinant.

%I A211156 #6 Jan 10 2017 22:06:58
%S A211156 37,293,817,2513,4677,10149,15873,28545,40581,65093,86769,128977,
%T A211156 164581,231173,285953,385153,464357,605477,715889,909201,1058501,
%U A211156 1315237,1510721,1844289,2095429
%N A211156 Number of 2 X 2 matrices having all terms in {-n,...,0,..,n} and even nonnegative determinant.
%C A211156 For a guide to related sequences, see A210000.
%t A211156 a = -n; b = n; z1 = 25;
%t A211156 t[n_] := t[n] = Flatten[Table[w*z - x*y, {w, a, b}, {x, a, b}, {y, a, b}, {z, a, b}]]
%t A211156 c[n_, k_] := c[n, k] = Count[t[n], k]
%t A211156 u[n_] := u[n] = Sum[c[n, 2 k], {k, 0, 2*n^2}]
%t A211156 v[n_] := v[n] = Sum[c[n, 2 k], {k, 1, 2*n^2}]
%t A211156 w[n_] := w[n] = Sum[c[n, 2 k - 1], {k, 1, 2*n^2}]
%t A211156 u1 = Table[u[n], {n, 1, z1}] (* A211156 *)
%t A211156 v1 = Table[v[n], {n, 1, z1}] (* A211157 *)
%t A211156 w1 = Table[w[n], {n, 1, z1}] (* A211158 *)
%t A211156 (u1 - 1)/4 (* integers *)
%t A211156 v1/4 (* integers *)
%t A211156 w1/4 (* integers *)
%Y A211156 Cf. A210000.
%K A211156 nonn
%O A211156 1,1
%A A211156 _Clark Kimberling_, Apr 05 2012