0,1

If you choose to adjoin a top and a bottom element to each resulting lattice, you must add 2 to these cardinalities: see A137400.

G. Birkoff, Lattice Theory, American Mathematical Society, third edition (1967), pp. 63-64 [for the case n = 1].

M. P. Schutzenberger, Construction du treillis modulaire engendre par deux elements et une chaine finie discrete, Comptes Rendus de lAcad. Sci. Paris, vol. 235 (1952), pp. 926-928.

K. Takeuchi, On free modular lattices II, Tohoku Mathematical Journal (2), vol. 11 (1959), pp. 1-12 [for the case n = 2].

When n = 0, the lattice consists of the two elements, their meet and their join, so a(0) = 4. When n = 1, we get the free modular lattice generated by three elements, so a(1) = 28.

Sequence in context: A058227 A131459 A139736 this_sequence A051536 A043013 A145544

Adjacent sequences: A128938 A128939 A128940 this_sequence A128942 A128943 A128944

nonn

Lyle Ramshaw (lyle.ramshaw(AT)hp.com), Apr 08 2008