A278691 - OEIS

A278691

Number of graded lattices on n nodes.

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

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).

KEYWORD

nonn,more

AUTHOR

EXTENSIONS

a(16)-a(21) from Kohonen (2017), by Jukka Kohonen, Aug 15 2017

STATUS

approved