login
A321035
Number of words of length 3n such that all letters of the quinary 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
273, 15300, 564585, 17493938, 495445275, 13337746758, 348484836788, 8943435290790, 227093583305420, 5731575551864799, 144208756776131553, 3624029726937528334, 91079326041351533935, 2291027079046386970458, 57709725323735510918970, 1456179679670608615334480
OFFSET
5,1
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))(5):
seq(a(n), n=5..25);
CROSSREFS
Column k=5 of A256311.
Sequence in context: A279114 A210270 A351766 * A225702 A307537 A295455
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Oct 26 2018
STATUS
approved