A258496 Number of words of length 2n such that all letters of the nonary 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.

4862, 629850, 47432550, 2728352253, 133216751525, 5829093450180, 236006398327050, 9025008152896320, 330547676678287002, 11710509049983422030, 404211829411082901714, 13667296618312167097605, 454559414725395785663741, 14918526141220986683667840

Offset

9,1

Links

Alois P. Heinz, Table of n, a(n) for n = 9..650

Formula

a(n) ~ 32^n / (246960*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, 9):
seq(a(n), n=9..25);

Crossrefs

Column k=9 of A256117.

Sequence in context: A124088 A244106 A264182 * A258397 A215549 A295442

Adjacent sequences: A258493 A258494 A258495 * A258497 A258498 A258499

Keyword

nonn

Author

Alois P. Heinz, May 31 2015

Status

approved