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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

Table of n, a(n) for n=2..14.

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: A055084 A005461 A138443 * A016158 A335509 A193701

Adjacent sequences:  A235452 A235453 A235454 * A235456 A235457 A235458

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 November 27 16:35 EST 2021. Contains 349394 sequences. (Running on oeis4.)