A321040 Number of words of length 3n such that all letters of the denary 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.

1430715, 385671000, 59757446980, 7005490433656, 691555233881785, 60757817462444531, 4909804407096952946, 372791285261732999200, 26986460830582840320825, 1882051044395835159556710, 127426007577261157375345878, 8424538202077517861490125956

Offset

10,1

Links

Alois P. Heinz, Table of n, a(n) for n = 10..566

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))(10):
seq(a(n), n=10..25);

Crossrefs

Column k=10 of A256311.

Sequence in context: A054852 A242824 A204288 * A345614 A346331 A345624

Adjacent sequences: A321037 A321038 A321039 * A321041 A321042 A321043

Keyword

nonn

Author

Alois P. Heinz, Oct 26 2018

Status

approved