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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.)