

A211066


Number of 2 X 2 matrices having all terms in {1,...,n} and nonnegative even determinant.


4



1, 8, 28, 96, 193, 448, 728, 1360, 1985, 3264, 4420, 6696, 8641, 12296, 15360, 20896, 25361, 33344, 39636, 50680, 59289, 74056, 85376, 104728, 119377, 144032, 162588, 193568, 216585, 254880, 283096, 329656, 363881, 419856, 460804
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OFFSET

1,2


COMMENTS

For a guide to related sequences, see A210000.


LINKS



FORMULA



MATHEMATICA

a = 1; b = n; z1 = 35;
t[n_] := t[n] = Flatten[Table[w*z  x*y, {w, a, b}, {x, a, b}, {y, a, b}, {z, a, b}]]
c[n_, k_] := c[n, k] = Count[t[n], k]
u[n_] := u[n] = Sum[c[n, 2 k], {k, 0, n^2}]
v[n_] := v[n] = Sum[c[n, 2 k], {k, 1, n^2}]
w[n_] := w[n] = Sum[c[n, 2 k  1], {k, 1, n^2}]
Table[u[n], {n, 1, z1}] (* A211066 *)
Table[v[n], {n, 1, z1}] (* A211067 *)
Table[w[n], {n, 1, z1}] (* A211068 *)


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



