

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



43263, 7104240, 694377450, 52825297536, 3463906615356, 206132702914710, 11470240358743842, 608199451197152100, 31120996552066805175, 1550313320809537870320, 75665062766954753664390, 3635046065217379316477688, 172499755061750807257325550
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OFFSET

8,1


LINKS



MAPLE

b:= (n, k)> `if`(n=0, 1, k/n*add(binomial(3*n, j)*(nj)*(k1)^j, j=0..n1)):
a:= n> (k> add((1)^i*b(n, ki)/(i!*(ki)!), i=0..k))(8):
seq(a(n), n=8..25);


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



