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A183763 Number of 2 X 2 nonsingular 0..n matrices with a(1,1) <= a(1,2) <= a(2,1) <= a(2,2). 0
1, 6, 19, 44, 89, 158, 263, 408, 606, 867, 1208, 1629, 2162, 2807, 3584, 4510, 5615, 6893, 8394, 10107, 12076, 14321, 16874, 19723, 22938, 26527, 30517, 34930, 39831, 45188, 51109, 57563, 64616, 72301, 80642, 89657, 99462, 110027, 121404, 133613 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Singular matrices = binomial(n+4,4) - a(n).

LINKS

Table of n, a(n) for n=1..40.

EXAMPLE

All solutions for n=2:

..0..1....0..2....1..1....0..1....1..2....0..1

..1..1....2..2....1..2....2..2....2..2....1..2

CROSSREFS

Sequence in context: A005900 A138357 A299264 * A209403 A272707 A266938

Adjacent sequences:  A183760 A183761 A183762 * A183764 A183765 A183766

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jan 06 2011

STATUS

approved

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Last modified February 24 23:02 EST 2018. Contains 299629 sequences. (Running on oeis4.)