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A321034 Number of words of length 3n such that all letters of the quaternary 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
55, 1820, 42228, 859180, 16482191, 307525140, 5665789450, 103894641488, 1904303218783, 34970000393120, 644169388645755, 11909742222826580, 221052371765382039, 4118875328648495940, 77037256813624307478, 1446046251457910719288, 27235202791173787953695 (list; graph; refs; listen; history; text; internal format)
OFFSET
4,1
LINKS
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))(4):
seq(a(n), n=4..25);
CROSSREFS
Column k=4 of A256311.
Sequence in context: A166833 A004352 A163722 * A275942 A217758 A346325
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Oct 26 2018
STATUS
approved

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Last modified June 15 03:12 EDT 2024. Contains 373402 sequences. (Running on oeis4.)