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A056280 Number of primitive (aperiodic) word structures of length n which contain exactly four different symbols. 2
0, 0, 0, 1, 10, 65, 350, 1700, 7770, 34095, 145750, 611435, 2532530, 10391395, 42355940, 171797200, 694337290, 2798799150, 11259666950, 45232081795, 181509069700, 727778478075, 2916342574750, 11681056021300 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

COMMENTS

Permuting the alphabet will not change a word structure. Thus aabc and bbca have the same structure.

REFERENCES

M. R. Nester (1999). Mathematical investigations of some plant interaction designs. PhD Thesis. University of Queensland, Brisbane, Australia. [See A056391 for pdf file of Chap. 2]

LINKS

Table of n, a(n) for n=1..24.

FORMULA

a(n) = Sum_{n > 0, d|n} mu(d)*A000453(n/d).

CROSSREFS

Column 4 of A137651.

Cf. A056269.

Sequence in context: A092441 A022638 A003519 * A000453 A291231 A097791

Adjacent sequences:  A056277 A056278 A056279 * A056281 A056282 A056283

KEYWORD

nonn

AUTHOR

Marks R. Nester

STATUS

approved

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Last modified February 20 20:12 EST 2018. Contains 299385 sequences. (Running on oeis4.)