Number of n-celled polyominoes with exactly 4 holes.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =0a(8) =0a(9) =0a(10) =0a(11) =0a(12) =0a(13) =0a(14) =0a(15) =0a(16) =8a(17) =179a(18) =2509a(19) =25609a(20) =214932a(21) =1578984a(22) =10536260a(23) =65411645a(24) =383981499a(25) =2156114468a(26) =11678888362a(27) =61413242603