A373894 Number of self-dual lattices on n unlabeled nodes.

1, 1, 1, 1, 2, 3, 7, 13, 36, 76, 232, 562, 1860, 5025

Offset: 0

Author

Jukka Kohonen, Jun 21 2024

Keywords

• nonn
• more
• hard

Comments

Lattices whose Hasse diagram looks the same if it is turned upside down.

Examples

			a(5)=3: These are the three lattices.
  o      o        o
  |     / \      /|\
  o    o   |    o o o
  |    |   o     \|/
  o    o   |      o
  |     \ /
  o      o
  |
  o
		

Links

• Volker Gebhardt and Stephen Tawn, Catalogue of unlabelled lattices on up to 16 elements, Western Sydney University (2018).

Crossrefs

Cf. A006966 (lattices), A133983 (self-dual posets).

Programs

Sage

sum(L.is_lattice() and L.is_self_dual() for L in Posets(n))