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A209979 Number of unimodular 2 X 2 matrices having all elements in {1,2,...,n}. 2
0, 0, 4, 16, 28, 56, 68, 112, 140, 184, 212, 288, 316, 408, 452, 512, 572, 696, 740, 880, 940, 1032, 1108, 1280, 1340, 1496, 1588, 1728, 1820, 2040, 2100, 2336, 2460, 2616, 2740, 2928, 3020, 3304, 3444, 3632, 3756, 4072, 4164, 4496, 4652, 4840 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Equivalently, the number of 2 X 2 matrices having all elements in {1,2,...,n} and having an inverse whose elements are all integers.

See A210000 for a guide to related sequences.

LINKS

Table of n, a(n) for n=0..45.

MATHEMATICA

(See the Mathematica section at A210000.)

CROSSREFS

Cf. A210000.

Sequence in context: A121054 A332044 A273368 * A294629 A160410 A256534

Adjacent sequences:  A209976 A209977 A209978 * A209980 A209981 A209982

KEYWORD

nonn

AUTHOR

Clark Kimberling, Mar 16 2012

STATUS

approved

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Last modified April 8 21:00 EDT 2020. Contains 333325 sequences. (Running on oeis4.)