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A056268
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Number of primitive (aperiodic) words of length n which contain exactly three different symbols.
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1
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0, 0, 6, 36, 150, 534, 1806, 5760, 18144, 55830, 171006, 518580, 1569750, 4732014, 14250450, 42844320, 128746950, 386615376, 1160688606, 3483582660, 10454059938, 31368305694, 94118013006, 282378679920, 847187946000, 2541662931990, 7625194813656, 22875982414740
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OFFSET
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1,3
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REFERENCES
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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]
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LINKS
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FORMULA
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a(n) = Sum_{d|n} mu(d)*A001117(n/d).
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PROG
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(PARI) f(n) = 3^n - 3*2^n + 3;
a(n) = sumdiv(n, d, moebius(d)*f(n/d)); \\ Michel Marcus, Mar 25 2022
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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