|
Search: id:A087729
|
|
|
| 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. |
|
+0
1
|
|
| 1, 1, 1, 2, 2, 3, 5, 8, 11, 18, 29, 49, 83, 148, 267, 507, 977, 1958, 4041, 8626, 18942
(list; graph; listen)
|
|
|
OFFSET
|
1,4
|
|
|
COMMENT
|
a(21) took about 78 hours to compute on a fast DEC alpha (using MAGMA).
|
|
EXAMPLE
|
a(5) = 2 because the only example up to permutation are {{},{1},{2},{1,2},{3}} {{},{1},{2},{3},{4}}.
|
|
CROSSREFS
|
Sequence in context: A111181 A076777 A111123 this_sequence A039890 A152948 A018136
Adjacent sequences: A087726 A087727 A087728 this_sequence A087730 A087731 A087732
|
|
KEYWORD
|
hard,more,nonn,nice
|
|
AUTHOR
|
Victor S. Miller (victor(AT)idaccr.org), Sep 30 2003
|
|
|
Search completed in 0.002 seconds
|
