A055531 Number of labeled order relations on n nodes in which longest chain has 2 nodes.

2, 12, 86, 840, 11642, 227892, 6285806, 243593040, 13262556722, 1014466283292, 109128015915206, 16521353903210520, 3524056001906654762, 1059868947134489801412, 449831067019305308555486, 269568708630308018001547680, 228228540531327778410439620962

Offset

2,1

References

L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 60.

Links

Table of n, a(n) for n=2..18.

Formula

a(n) = A001831(n)-1.

a(n) = Sum_{k=1..n-1} binomial(n,k)*(2^(n-k)-1)^k. - Geoffrey Critzer, Oct 29 2023

Crossrefs

A column or diagonal of triangle in A342587.

Cf. A001831, A052296.

Sequence in context: A372104 A097237 A363255 * A305209 A290568 A181345

Adjacent sequences: A055528 A055529 A055530 * A055532 A055533 A055534

Keyword

easy,nonn

Author

N. J. A. Sloane, Jul 10 2000

Extensions

More terms from Vladeta Jovovic, Oct 24 2000

a(13)-a(16) corrected and more terms from Sean A. Irvine, Mar 25 2022

Status

approved