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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 (list; graph; refs; listen; history; text; internal format)
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), 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

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

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Last modified October 18 05:17 EDT 2018. Contains 316304 sequences. (Running on oeis4.)