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

Offset: 1

Author

R. H. Hardin, May 10 2010

Keywords

• nonn

Links

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

Crossrefs

Column k=0 of A242820.

Columns k=8,14 of A242784.

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

Extensions

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