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

Author

Heinrich Ludwig, Jan 12 2014

Keywords

• nonn
• more

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.

Examples

			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)

Extensions

a(13), a(14) from Heinrich Ludwig, Nov 16 2016