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A373894
Number of self-dual lattices on n unlabeled nodes.
1
1, 1, 1, 1, 2, 3, 7, 13, 36, 76, 232, 562, 1860, 5025
OFFSET
0,5
COMMENTS
Lattices whose Hasse diagram looks the same if it is turned upside down.
LINKS
Volker Gebhardt and Stephen Tawn, Catalogue of unlabelled lattices on up to 16 elements, Western Sydney University (2018).
EXAMPLE
a(5)=3: These are the three lattices.
o o o
| / \ /|\
o o | o o o
| | o \|/
o o | o
| \ /
o o
|
o
PROG
(Sage) sum(L.is_lattice() and L.is_self_dual() for L in Posets(n))
CROSSREFS
Cf. A006966 (lattices), A133983 (self-dual posets).
Sequence in context: A123408 A033995 A345247 * A013917 A371181 A293994
KEYWORD
nonn,more,hard
AUTHOR
Jukka Kohonen, Jun 21 2024
STATUS
approved