Number of n-celled free polyominoes with 1 hole.

Terms

a(0) =1a(1) =6a(2) =37a(3) =195a(4) =975a(5) =4622a(6) =21128a(7) =94109a(8) =410820a(9) =1766591a(10) =7506179a(11) =31596240a(12) =131991619a(13) =547992183a(14) =2263477612a(15) =9309386178a(16) =38150082057a(17) =155859235424a(18) =635067478628