Number of directed column-convex polyominoes having at least one 1-cell column.

Terms

a(0) =1a(1) =1a(2) =4a(3) =10a(4) =28a(5) =75a(6) =202a(7) =540a(8) =1440a(9) =3828a(10) =10153a(11) =26875a(12) =71021a(13) =187421a(14) =494013a(15) =1300844a(16) =3422509a(17) =8998118a(18) =23642479a(19) =62088032a(20) =162978242a(21) =427648023a(22) =1121766397a(23) =2941697012a(24) =7712415568a(25) =20215976824a(26) =52981414253a(27) =138831400836