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A183764 Number of 2 X 2 singular 0..n matrices with a(1,1) <= a(1,2) <= a(2,1) <= a(2,2). 1
4, 9, 16, 26, 37, 52, 67, 87, 109, 134, 157, 191, 218, 253, 292, 335, 370, 422, 461, 519, 574, 629, 676, 752, 813, 878, 948, 1030, 1089, 1188, 1251, 1342, 1429, 1514, 1609, 1733, 1808, 1903, 2006, 2138, 2221, 2362, 2449, 2579, 2721, 2836, 2931, 3102, 3222 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..200

EXAMPLE

All solutions for n=2:

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

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

CROSSREFS

Sequence in context: A274963 A050461 A189835 * A022334 A073171 A328363

Adjacent sequences:  A183761 A183762 A183763 * A183765 A183766 A183767

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jan 06 2011

STATUS

approved

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Last modified October 18 01:39 EDT 2021. Contains 348065 sequences. (Running on oeis4.)