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A321039 Number of words of length 3n such that all letters of the nonary 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
246675, 52676325, 6567205788, 627427976340, 51015901999920, 3724987212716133, 252083271295845990, 16134288197281838562, 990146359650754095405, 58830559749207291469515, 3408249740757631887365820, 193544431133535679583811150, 10816879949695374764949152976 (list; graph; refs; listen; history; text; internal format)
OFFSET

9,1

LINKS

Alois P. Heinz, Table of n, a(n) for n = 9..583

MAPLE

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

a:= n-> (k-> add((-1)^i*b(n, k-i)/(i!*(k-i)!), i=0..k))(9):

seq(a(n), n=9..25);

CROSSREFS

Column k=9 of A256311.

Sequence in context: A251856 A146544 A237313 * A230525 A052198 A053077

Adjacent sequences:  A321036 A321037 A321038 * A321040 A321041 A321042

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Oct 26 2018

STATUS

approved

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Last modified January 26 13:18 EST 2021. Contains 340439 sequences. (Running on oeis4.)