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.

1, 15, 181, 1253, 6044, 22302, 68661, 183645, 439578, 964938, 1974128, 3801457, 6966581

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: A005461 A373759 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