A352367 Row sums of A352366.

1, 1, 2, 6, 23, 105, 552, 3276, 21632, 157058, 1241542, 10599358, 97078720, 948631866, 9844060930, 108045790170, 1249891268947, 15192207346713, 193489732812832, 2575819322454708, 35763019798305487, 516830453606687539, 7760160395056532042, 120860540786892879030

Offset

0,3

Comments

a(n) is the number of chordal graphs with fixed symmetric perfect elimination ordering; i.e., graphs on V = [n] such that 1,...,n and n,...,1 are perfect elimination orderings. - Robert Lauff, Jan 25 2023

a(n) is the number of labeled unit-interval-graphs. This is because connected labeled unit-interval-graphs are a Catalan family. Given a partition of [n], we draw a connected unit-interval-graph for each of the partition classes. This weights the partitions with a Catalan number. The connection to my previous comment can be shown by induction. - Robert Lauff, Feb 01 2023

Links

Table of n, a(n) for n=0..23.

Wikipedia, Chordal graph.

Crossrefs

Cf. A000108, A352366.

Sequence in context: A113227 A200406 A165489 * A192315 A325297 A288912

Adjacent sequences: A352364 A352365 A352366 * A352368 A352369 A352370

Keyword

nonn

Author

Peter Luschny, Mar 15 2022

Status

approved