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
KEYWORD
nonn,more,hard
AUTHOR
Jukka Kohonen, Jun 21 2024
STATUS
approved