A210285 - OEIS

%I #9 Nov 25 2016 12:21:57

%S 1,10,7,15,36,52,65,89,155,179,153,193,374,422,287,319,617,681,584,

%T 656,914,962,639,727,1705,1785,889,961,1672,1784,1768,1888,2496,2576,

%U 1483,1579,3460,3604,1843,1939,4177,4337,3298,3466,3886,3982

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

%C See A210000 for a guide to related sequences.

%H Chai Wah Wu, <a href="/A210285/b210285.txt">Table of n, a(n) for n = 0..3000</a>

%t a = 0; b = n; z1 = 45;

%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 Table[c[n, Floor[n/2]], {n, 0, z1}]   (* A210285 *)

%Y Cf. A210000.

%K nonn

%O 0,2

%A _Clark Kimberling_, Mar 19 2012