A235455 - OEIS

%I #12 Nov 16 2016 15:52:29

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

%T 6966581

%N 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.

%C Column 4 of A235453.

%C Also number of non-equivalent complete quadrangles on an n X n grid.

%C Without the restriction "non-equivalent (mod D_4)" the numbers are given by A175383, n >= 2.

%e There are a(3) = 15 non-equivalent ways to place 4 points (X) on a 3 X 3 grid. Examples are:

%e   X . X    . X .    X X .

%e   . . .    X . X    X . .

%e   X . X    . X .    . . X

%Y Cf. A235453, A045996, A235454 (3 points), A235456 (5 points), A235457 (6 points), A235458 (7 points)

%K nonn,more

%O 2,2

%A _Heinrich Ludwig_, Jan 12 2014

%E a(13), a(14) from _Heinrich Ludwig_, Nov 16 2016