Number of convex polygons of perimeter 2n on square lattice.

Terms

a(0) =1a(1) =2a(2) =7a(3) =28a(4) =120a(5) =528a(6) =2344a(7) =10416a(8) =46160a(9) =203680a(10) =894312a(11) =3907056a(12) =16986352a(13) =73512288a(14) =316786960a(15) =1359763168a(16) =5815457184a(17) =24788842304a(18) =105340982248a(19) =446389242480