VOOZH about

URL: https://oeis.org/A258494

⇱ A258494 - OEIS

login
A258494
Number of words of length 2n such that all letters of the septenary 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
429, 32032, 1447992, 51647700, 1605746373, 45730269662, 1227377689395, 31600247019120, 789604855530855, 19302666179660304, 464277874912868104, 11032638071392824348, 259801742258903758053, 6076538940891732415102, 141407795779400734204647
OFFSET
7,1
LINKS
FORMULA
a(n) ~ 24^n / (3000*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, 7):
seq(a(n), n=7..25);
CROSSREFS
Column k=7 of A256117.
Sequence in context: A264180 A393925 A270412 * A258395 A215547 A181195
KEYWORD
nonn
AUTHOR
Alois P. Heinz, May 31 2015
STATUS
approved