cp's OEIS Frontend

A211069 Number of 2 X 2 matrices having all terms in {1,...,n} and determinant in [-n,n].

%I A211069 #6 Jan 14 2017 01:37:22
%S A211069 1,14,57,150,309,574,921,1444,2091,2952,3919,5314,6709,8534,10603,
%T A211069 13102,15593,18962,22133,26332,30569,35346,40097,46690,52553,59394,
%U A211069 66603,75094,82833,93282,102181,113422,124411,136412,148613
%N A211069 Number of 2 X 2 matrices having all terms in {1,...,n} and determinant in [-n,n].
%C A211069 For a guide to related sequences, see A210000.
%t A211069 a = 1; b = n; z1 = 35;
%t A211069 t[n_] := t[n] = Flatten[Table[w*z - x*y, {w, a, b}, {x, a, b}, {y, a, b}, {z, a, b}]]
%t A211069 c[n_, k_] := c[n, k] = Count[t[n], k]
%t A211069 c1[n_, m_] := c1[n, m] = Sum[c[n, k], {k, -n, m}]
%t A211069 Table[c1[n, n], {n, 1, z1}]  (* A211069 *)
%Y A211069 Cf. A210000.
%K A211069 nonn
%O A211069 1,2
%A A211069 _Clark Kimberling_, Mar 31 2012