cp's OEIS Frontend

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.

%I A321038 #4 Oct 26 2018 16:32:14
%S A321038 43263,7104240,694377450,52825297536,3463906615356,206132702914710,
%T A321038 11470240358743842,608199451197152100,31120996552066805175,
%U A321038 1550313320809537870320,75665062766954753664390,3635046065217379316477688,172499755061750807257325550
%N 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.
%H A321038 Alois P. Heinz, <a href="/A321038/b321038.txt">Table of n, a(n) for n = 8..602</a>
%p A321038 b:= (n, k)-> `if`(n=0, 1, k/n*add(binomial(3*n, j)*(n-j)*(k-1)^j, j=0..n-1)):
%p A321038 a:= n-> (k-> add((-1)^i*b(n, k-i)/(i!*(k-i)!), i=0..k))(8):
%p A321038 seq(a(n), n=8..25);
%Y A321038 Column k=8 of A256311.
%K A321038 nonn
%O A321038 8,1
%A A321038 _Alois P. Heinz_, Oct 26 2018