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A278691
Number of graded lattices on n nodes.
1
1, 1, 1, 2, 4, 9, 22, 60, 176, 565, 1980, 7528, 30843, 135248, 630004, 3097780, 15991395, 86267557, 484446620, 2822677523, 17017165987
OFFSET
1,4
COMMENTS
A finite lattice is graded if, for any element, all paths from the bottom to that element have the same length.
LINKS
J. Heitzig and J. Reinhold, Counting finite lattices, Algebra Universalis, 48 (2002), 43-53.
J. Kohonen, Generating modular lattices up to 30 elements, arXiv:1708.03750 [math.CO] preprint (2017).
M. Malandro, The unlabeled lattices on <=15 nodes, (listing of lattices; graded lattices are a subset of these).
CROSSREFS
Cf. A006966 (lattices), A229202 (semimodular lattices).
Sequence in context: A293854 A271078 A292790 * A159329 A159334 A159330
KEYWORD
nonn,more
AUTHOR
Jukka Kohonen, Nov 26 2016
EXTENSIONS
a(16)-a(21) from Kohonen (2017), by Jukka Kohonen, Aug 15 2017
STATUS
approved