A279292 Number of permutations of [n] having exactly three (possibly overlapping) doubledescents.

1, 10, 167, 2064, 28143, 374166, 5227491, 75105984, 1127851278, 17625022976, 287569327286, 4891520843344, 86749331150517, 1602239541108282, 30795187124606301, 615261376037422992, 12764913390565572333, 274721686459213597782, 6126847681304067647287

Offset: 5

Author

Alois P. Heinz, Dec 09 2016

Keywords

• nonn

Links

• Alois P. Heinz, Table of n, a(n) for n = 5..462

Crossrefs

Column k=3 of A162975.

Formula

a(n) ~ c * 3^(3*n/2) * n^(n+7/2) / (exp(n) * 2^n * Pi^n), where c = 0.0065517603957816327489026... . - Vaclav Kotesovec, Dec 11 2016