Number of strictly 2-dimensional one-sided polyominoes with n cells.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =6a(5) =17a(6) =59a(7) =195a(8) =703a(9) =2499a(10) =9188a(11) =33895a(12) =126758a(13) =476269a(14) =1802311a(15) =6849776a(16) =26152417a(17) =100203193a(18) =385221142a(19) =1485200847a(20) =5741256763a(21) =22245940544a(22) =86383382826a(23) =336093325057