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A185652 Number of permutations of [n] having a shortest ascending run of length 2. 3
0, 0, 1, 0, 5, 18, 89, 519, 3853, 27555, 233431, 2167152, 21596120, 232817282, 2718706924, 33814848445, 448311181346, 6319365554730, 94225534689624, 1481940898130323, 24536143182460549, 426432943716156580, 7762187693343502658, 147704506384475066381 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,5

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..150

FORMULA

a(n) ~ c * (3*sqrt(3)/(2*Pi))^n * n!, where c = 0.45178068752734823... . - Vaclav Kotesovec, Sep 06 2014

EXAMPLE

a(2) = 1: 12.

a(4) = 5: 1324, 1423, 2314, 2413, 3412.

a(5) = 18: 12435, 12534, 13245, 13425, 13524, 14235, 14523, 15234, 23145, 23415, 23514, 24135, 24513, 25134, 34125, 34512, 35124, 45123.

CROSSREFS

Column k=2 of A064315.

Sequence in context: A213190 A151490 A282475 * A009305 A097574 A113023

Adjacent sequences:  A185649 A185650 A185651 * A185653 A185654 A185655

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Aug 29 2013

STATUS

approved

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Last modified September 15 02:19 EDT 2019. Contains 327062 sequences. (Running on oeis4.)