%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 nonequivalent (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 nonequivalent complete quadrangles on an n X n grid.
%C Without the restriction "nonequivalent (mod D_4)" the numbers are given by A175383, n >= 2.
%e There are a(3) = 15 nonequivalent 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
