Number of directed column-convex polyominoes with perimeter 2n+2.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =20a(5) =71a(6) =263a(7) =1005a(8) =3933a(9) =15684a(10) =63505a(11) =260390a(12) =1079019a(13) =4511700a(14) =19011521a(15) =80653480a(16) =344193353a(17) =1476589475a(18) =6364258163a(19) =27545933212a(20) =119676949397a(21) =521739175908