A209991 - OEIS

%I #10 Oct 23 2018 16:15:53

%S 1,13,38,79,136,209,302,407,536,681,846,1015,1240,1441,1678,1951,2240,

%T 2505,2854,3151,3552,3945,4326,4687,5216,5657,6110,6615,7192,7649,

%U 8342,8831,9472,10105,10702,11407,12272,12857,13526,14279,15224

%N Number of 2 X 2 matrices with all elements in {0,1,...,n} and determinant in {0,1}.

%C See A210000 for a guide to related sequences.

%F A059306 + A171503.

%t a = 0; b = n; z1 = 40;

%t t[n_] := t[n] = Flatten[Table[w*z - x*y, {w, a, b}, {x, a, b}, {y, a, b}, {z, a, b}]]

%t c[n_, k_] := c[n, k] = Count[t[n], k]

%t c1[n_, m_] := c1[n, m] = Sum[c[n, k], {k, 0, 1}]

%t Table[c1[n, 1], {n, 0, z1}]    (* A209991 *)

%Y Cf. A059306, A171503, A210000.

%K nonn

%O 0,2

%A _Clark Kimberling_, Mar 18 2012