Canonically 2-indecomposable posets with n antichains.

Terms

a(0) =0a(1) =1a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =2a(8) =1a(9) =1a(10) =0a(11) =7a(12) =5a(13) =16a(14) =14a(15) =40a(16) =41a(17) =120a(18) =131a(19) =321a(20) =402a(21) =901a(22) =1210a(23) =2590a(24) =3621a(25) =7371a(26) =10841a(27) =21178a(28) =32222a(29) =61273