

A278691


Number of graded lattices on n nodes.


0



1, 1, 1, 2, 4, 9, 22, 60, 176, 565, 1980, 7528, 30843, 135248, 630004, 3097780, 15991395, 86267557, 484446620, 2822677523, 17017165987
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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

Table of n, a(n) for n=1..21.
J. Heitzig and J. Reinhold, Counting finite lattices, Algebra Universalis, 48 (2002), 4353.
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
Adjacent sequences: A278688 A278689 A278690 * A278692 A278693 A278694


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



