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.

55, 1820, 42228, 859180, 16482191, 307525140, 5665789450, 103894641488, 1904303218783, 34970000393120, 644169388645755, 11909742222826580, 221052371765382039, 4118875328648495940, 77037256813624307478, 1446046251457910719288, 27235202791173787953695

Offset

4,1

Links

Alois P. Heinz, Table of n, a(n) for n = 4..770

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

Adjacent sequences: A321031 A321032 A321033 * A321035 A321036 A321037

Keyword

nonn

Author

Alois P. Heinz, Oct 26 2018

Status

approved