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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.
2
1430, 143208, 8488440, 389948856, 15390120042, 549818906780, 18329867191350, 581350326663600, 17769492060922914, 528200606751594392, 15368894406877386408, 439845149792754810984, 12426477142114470011642, 347532158068343623121916, 9642227504194296532321086
OFFSET
8,1
LINKS
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
KEYWORD
nonn
AUTHOR
Alois P. Heinz, May 31 2015
STATUS
approved