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A235455 Number of non-equivalent (mod D_4) ways to arrange 4 points on an n X n square grid so that no three points are collinear. 6
1, 15, 181, 1253, 6044, 22302, 68661, 183645, 439578, 964938, 1974128, 3801457, 6966581 (list; graph; refs; listen; history; text; internal format)
OFFSET
2,2
COMMENTS
Column 4 of A235453.
Also number of non-equivalent complete quadrangles on an n X n grid.
Without the restriction "non-equivalent (mod D_4)" the numbers are given by A175383, n >= 2.
LINKS
EXAMPLE
There are a(3) = 15 non-equivalent ways to place 4 points (X) on a 3 X 3 grid. Examples are:
X . X . X . X X .
. . . X . X X . .
X . X . X . . . X
CROSSREFS
Cf. A235453, A045996, A235454 (3 points), A235456 (5 points), A235457 (6 points), A235458 (7 points)
Sequence in context: A005461 A373759 A138443 * A016158 A335509 A193701
KEYWORD
nonn,more
AUTHOR
Heinrich Ludwig, Jan 12 2014
EXTENSIONS
a(13), a(14) from Heinrich Ludwig, Nov 16 2016
STATUS
approved

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Last modified June 25 11:18 EDT 2024. Contains 373701 sequences. (Running on oeis4.)