A178008 Number of permutations of 1..n with no element e[i>=2]<e[1+floor((i-2)/3)] (3-way heap).

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

0,4

Links

Alois P. Heinz, Table of n, a(n) for n = 0..502

Wikipedia, D-ary heap

Crossrefs

Simple 2-way heap A056971.

Column k=3 of A273693.

Sequence in context: A094261 A080497 A127724 * A266005 A056744 A344184

Adjacent sequences: A178005 A178006 A178007 * A178009 A178010 A178011

Keyword

nonn

Author

R. H. Hardin, May 17 2010

Extensions

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

Status

approved