A279293 Number of permutations of [n] having exactly four (possibly overlapping) doubledescents.

1, 12, 316, 4961, 88482, 1456780, 24970807, 430069638, 7646066285, 139512608803, 2630205520242, 51191324887317, 1030225266241718, 21431850533761458, 460916811387051427, 10243049068068285706, 235127217600172319772, 5571780677576178939683

Offset: 6

Author

Alois P. Heinz, Dec 09 2016

Keywords

• nonn

Links

• Alois P. Heinz, Table of n, a(n) for n = 6..461

Crossrefs

Column k=4 of A162975.

Formula

a(n) ~ c * 3^(3*n/2) * n^(n + 9/2) / (exp(n) * 2^n * Pi^n), where c = 0.000357063672536829943422824320618... . - Vaclav Kotesovec, Dec 22 2020