A177518 - OEIS

A177518

Number of permutations of 1..n avoiding adjacent step pattern up, down, down, down.

1, 2, 6, 24, 116, 672, 4536, 34944, 302896, 2916992, 30899616, 357080064, 4470310976, 60269056512, 870591770496, 13414154256384, 219604379097856, 3806644208863232, 69650568655858176, 1341477655028219904, 27128858382696129536, 574755293400886321152

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OFFSET

1,2

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..175

FORMULA

a(n) ~ c * n! / r^n, where r = 1.03841563726655630653502212237531835609230623619708108964... is the root of the equation cos(r) - sin(r) + exp(-r) = 0, and c = 1.1718801964367046779834894478269895859267745270209175... . - Vaclav Kotesovec, Aug 21 2014

CROSSREFS

Column k=0 of A242820.

Columns k=8,14 of A242784.

Sequence in context: A324131 A221988 A329788 * A369832 A319027 A228397

Adjacent sequences: A177515 A177516 A177517 * A177519 A177520 A177521

KEYWORD

nonn

AUTHOR

R. H. Hardin, May 10 2010

EXTENSIONS

a(18)-a(22) from Alois P. Heinz, Oct 06 2013

STATUS

approved