This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A235455 #12 Nov 16 2016 15:52:29 %S A235455 1,15,181,1253,6044,22302,68661,183645,439578,964938,1974128,3801457, %T A235455 6966581 %N 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. %C A235455 Column 4 of A235453. %C A235455 Also number of non-equivalent complete quadrangles on an n X n grid. %C A235455 Without the restriction "non-equivalent (mod D_4)" the numbers are given by A175383, n >= 2. %e A235455 There are a(3) = 15 non-equivalent ways to place 4 points (X) on a 3 X 3 grid. Examples are: %e A235455 X . X . X . X X . %e A235455 . . . X . X X . . %e A235455 X . X . X . . . X %Y A235455 Cf. A235453, A045996, A235454 (3 points), A235456 (5 points), A235457 (6 points), A235458 (7 points) %K A235455 nonn,more %O A235455 2,2 %A A235455 _Heinrich Ludwig_, Jan 12 2014 %E A235455 a(13), a(14) from _Heinrich Ludwig_, Nov 16 2016