A258495 Number of words of length 2n such that all letters of the octonary alphabet occur at least once and are introduced in ascending order and which can be built by repeatedly inserting doublets into the initially empty word.

1430, 143208, 8488440, 389948856, 15390120042, 549818906780, 18329867191350, 581350326663600, 17769492060922914, 528200606751594392, 15368894406877386408, 439845149792754810984, 12426477142114470011642, 347532158068343623121916, 9642227504194296532321086

Offset

8,1

Links

Alois P. Heinz, Table of n, a(n) for n = 8..650

Formula

a(n) ~ 28^n / (25920*sqrt(Pi)*n^(3/2)). - Vaclav Kotesovec, Jun 01 2015

Maple

A:= proc(n, k) option remember; `if`(n=0, 1, k/n*
      add(binomial(2*n, j)*(n-j)*(k-1)^j, j=0..n-1))
    end:
T:= (n, k)-> add((-1)^i*A(n, k-i)/(i!*(k-i)!), i=0..k):
a:= n-> T(n, 8):
seq(a(n), n=8..25);

Crossrefs

Column k=8 of A256117.

Sequence in context: A244105 A264181 A064305 * A258396 A215548 A274253

Adjacent sequences: A258492 A258493 A258494 * A258496 A258497 A258498

Keyword

nonn

Author

Alois P. Heinz, May 31 2015

Status

approved