Number of fixed polyominoes of area n with holes.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =4a(7) =41a(8) =272a(9) =1516a(10) =7708a(11) =37024a(12) =171188a(13) =770552a(14) =3400792a(15) =14787246a(16) =63558507a(17) =270697012a(18) =1144428004a(19) =4809192667a(20) =20108709174a(21) =83729183824a(22) =347400400426