A321036 Number of words of length 3n such that all letters of the senary 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.

1428, 122094, 6577494, 288152280, 11263151718, 410775452736, 14329297278912, 485304167135463, 16110681501126303, 527563895500327686, 17115058041339933282, 551744934193726332360, 17712851478876415128930, 567151641983253355425936, 18132410018268844312487352

Offset

6,1

Links

Alois P. Heinz, Table of n, a(n) for n = 6..659

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))(6):
seq(a(n), n=6..25);

Crossrefs

Column k=6 of A256311.

Sequence in context: A260283 A156853 A292704 * A094230 A353080 A238136

Adjacent sequences: A321033 A321034 A321035 * A321037 A321038 A321039

Keyword

nonn

Author

Alois P. Heinz, Oct 26 2018

Status

approved