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A209992 Number of 2 X 2 matrices with all elements in {1,2,...,n} and determinant in {0,1}. 2
0, 1, 8, 23, 46, 77, 120, 167, 230, 301, 384, 463, 590, 685, 808, 959, 1118, 1245, 1448, 1591, 1830, 2053, 2256, 2431, 2766, 3005, 3248, 3535, 3886, 4109, 4560, 4799, 5182, 5549, 5872, 6295, 6870, 7157, 7520, 7959, 8582 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

See A210000 for a guide to related sequences.

LINKS

Table of n, a(n) for n=0..40.

MATHEMATICA

a = 1; b = n; z1 = 40;

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, 0, 1}]

Table[c1[n, 1], {n, 0, z1}]   (* A209992 *)

CROSSREFS

Cf. A210000.

Sequence in context: A178072 A185257 A033951 * A212118 A175346 A225280

Adjacent sequences:  A209989 A209990 A209991 * A209993 A209994 A209995

KEYWORD

nonn

AUTHOR

Clark Kimberling, Mar 18 2012

STATUS

approved

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Last modified November 19 05:29 EST 2018. Contains 317333 sequences. (Running on oeis4.)