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A178008 Number of permutations of 1..n with no element e[i>=2]<e[1+floor((i-2)/3)] (3-way heap). 4
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified October 25 01:40 EDT 2021. Contains 348233 sequences. (Running on oeis4.)