%I
%S 0,3,6,9,12,18
%N Greatest number of edges in a simple polygon on an n X n grid with no two edges parallel or perpendicular.
%C a(8) >= 22, see picture in Links.
%H Giovanni Resta, <a href="/A271449/a271449.png">Illustration of a(3)a(7) and a(8) >= 22</a>
%e a(5)=9 because of this polygon on a 5 X 5 grid:
%e 2 . . . .
%e . . 1 3 5
%e . . 4 . 7
%e . 6 . . 8
%e 9 . . . .
%e See Links for other examples.
%Y Cf. A255981.
%K nonn,more
%O 2,2
%A _Giovanni Resta_, May 05 2016
