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A209993 Number of 2 X 2 matrices with all elements in {0,1,...,n} and determinant in {-1,0,1}. 0
1, 16, 45, 94, 159, 248, 349, 478, 623, 792, 973, 1182, 1423, 1672, 1933, 2238, 2559, 2888, 3261, 3630, 4063, 4504, 4925, 5374, 5935, 6456, 6957, 7534, 8159, 8728, 9453, 10062, 10767, 11480, 12141, 12942, 13855, 14584, 15325, 16174, 17183 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

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: A221593 A300962 A051868 * A322343 A318093 A223029

Adjacent sequences:  A209990 A209991 A209992 * A209994 A209995 A209996

KEYWORD

nonn

AUTHOR

Clark Kimberling, Mar 18 2012

STATUS

approved

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Last modified December 7 09:33 EST 2019. Contains 329843 sequences. (Running on oeis4.)