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A321041
Number of words of length 6n such that all letters of the n-ary 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
1, 1, 97, 29886, 16482191, 13337746758, 14329297278912, 19256258184412314, 31120996552066805175, 58830559749207291469515, 127426007577261157375345878, 311250333529456439224989700168, 846594239519776323268829614117536, 2538054216720547203941994076323844425
OFFSET
0,3
LINKS
FORMULA
a(n) = A256311(2n,n).
CROSSREFS
Cf. A256311.
Sequence in context: A233426 A173129 A306480 * A173354 A176135 A160489
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Oct 26 2018
STATUS
approved