Number of fixed polyominoes with n cells.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =19a(5) =63a(6) =216a(7) =760a(8) =2725a(9) =9910a(10) =36446a(11) =135268a(12) =505861a(13) =1903890a(14) =7204874a(15) =27394666a(16) =104592937a(17) =400795844a(18) =1540820542a(19) =5940738676a(20) =22964779660a(21) =88983512783a(22) =345532572678