A211069 - OEIS

A211069

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

1, 14, 57, 150, 309, 574, 921, 1444, 2091, 2952, 3919, 5314, 6709, 8534, 10603, 13102, 15593, 18962, 22133, 26332, 30569, 35346, 40097, 46690, 52553, 59394, 66603, 75094, 82833, 93282, 102181, 113422, 124411, 136412, 148613

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OFFSET

1,2

COMMENTS

For a guide to related sequences, see A210000.

LINKS

Table of n, a(n) for n=1..35.

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]

c1[n_, m_] := c1[n, m] = Sum[c[n, k], {k, -n, m}]

Table[c1[n, n], {n, 1, z1}] (* A211069 *)

CROSSREFS

Cf. A210000.

Sequence in context: A070741 A022286 A005915 * A212675 A041376 A063537

Adjacent sequences: A211066 A211067 A211068 * A211070 A211071 A211072

KEYWORD

nonn

AUTHOR

Clark Kimberling, Mar 31 2012

STATUS

approved