A274997 Number of permutations of [n] having exactly one doubledescent.

0, 0, 0, 1, 6, 41, 274, 2040, 16346, 143571, 1365354, 14056287, 155638724, 1847352720, 23400880036, 315270938501, 4502081195166, 67941159822229, 1080528172834710, 18065046986905320, 316769071197428286, 5813469963339136855, 111449225620923739458

Offset: 0

Author

Alois P. Heinz, Nov 29 2016

Keywords

• nonn

Links

• Alois P. Heinz, Table of n, a(n) for n = 0..463

Crossrefs

Column k=1 of A162975.

Formula

a(n) ~ c * 3^(3*n/2) * n^(n+3/2) / (exp(n) * 2^n * Pi^n), where c = 0.827206526063705458546024... . - Vaclav Kotesovec, Dec 11 2016