a(n) is the number of free convex polyominoes of n cells.

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =11a(5) =29a(6) =72a(7) =191a(8) =478a(9) =1211a(10) =2973a(11) =7274a(12) =17455a(13) =41645a(14) =98271a(15) =230848a(16) =539000a(17) =1254936