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A321038 Number of words of length 3n 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 triples of identical letters into the initially empty word. 2

%I

%S 43263,7104240,694377450,52825297536,3463906615356,206132702914710,

%T 11470240358743842,608199451197152100,31120996552066805175,

%U 1550313320809537870320,75665062766954753664390,3635046065217379316477688,172499755061750807257325550

%N Number of words of length 3n 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 triples of identical letters into the initially empty word.

%H Alois P. Heinz, <a href="/A321038/b321038.txt">Table of n, a(n) for n = 8..602</a>

%p b:= (n, k)-> `if`(n=0, 1, k/n*add(binomial(3*n, j)*(n-j)*(k-1)^j, j=0..n-1)):

%p a:= n-> (k-> add((-1)^i*b(n, k-i)/(i!*(k-i)!), i=0..k))(8):

%p seq(a(n), n=8..25);

%Y Column k=8 of A256311.

%K nonn

%O 8,1

%A _Alois P. Heinz_, Oct 26 2018

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Last modified January 25 01:10 EST 2021. Contains 340414 sequences. (Running on oeis4.)