Let X be the poset of finite subsets of the positive integers. The sequence is the number of downsets in X of cardinality n modulo equivalence by permutations of the positive integers.
A087729
Let X be the poset of finite subsets of the positive integers. The sequence is the number of downsets in X of cardinality n modulo equivalence by permutations of the positive integers.
Terms
- a(0) =1a(1) =1a(2) =1a(3) =2a(4) =2a(5) =3a(6) =5a(7) =8a(8) =11a(9) =18a(10) =29a(11) =49a(12) =83a(13) =148a(14) =267a(15) =507a(16) =977a(17) =1958a(18) =4041a(19) =8626a(20) =18942
External references
- oeis: A087729