A178008 Number of permutations of 1..n with no element e[i>=2]

1, 1, 1, 2, 6, 12, 40, 180, 630, 3360, 22680, 113400, 831600, 7484400, 38918880, 302702400, 2918916000, 20432412000, 205837632000, 2500927228800, 21598916976000, 263986763040000, 3837961401120000, 33774060329856000, 431557437548160000, 6658314750743040000

Offset: 0

Author

R. H. Hardin, May 17 2010

Keywords

• nonn

Comments

a(n) is also the number of labeled histories for the trifurcating labeled topology that possesses the largest number of labeled histories, among all labeled topologies with 2n+1 leaves. - Noah A Rosenberg, Feb 24 2025

Links

• Alois P. Heinz, Table of n, a(n) for n = 0..502
• E. H. Dickey, N. A. Rosenberg, Labelled histories with multifurcation and simultaneity, Phil. Trans. R. Soc. B 380 (2025), 20230307.
• Wikipedia, D-ary heap

Crossrefs

Simple 2-way heap A056971.

Column k=3 of A273693.

Extensions

a(0), a(21)-a(25) from Alois P. Heinz, May 27 2016