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A056278 Number of primitive (aperiodic) word structures of length n which contain exactly two different symbols. 4
0, 1, 3, 6, 15, 27, 63, 120, 252, 495, 1023, 2010, 4095, 8127, 16365, 32640, 65535, 130788, 262143, 523770, 1048509, 2096127, 4194303, 8386440, 16777200, 33550335, 67108608, 134209530, 268435455 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Permuting the alphabet will not change a word structure. Thus aabc and bbca have the same structure. This is identical to A000740 for n>1.

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..29.

FORMULA

Sum mu(d)*A000225(n/d-1) where d|n and n>0.

CROSSREFS

Apart from initial term, this is a duplicate of A000740.

Column 2 of A137651.

Cf. A056267.

Sequence in context: A134774 A264686 A165729 * A000740 A161625 A234848

Adjacent sequences:  A056275 A056276 A056277 * A056279 A056280 A056281

KEYWORD

nonn

AUTHOR

Marks R. Nester

STATUS

approved

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Last modified July 13 07:30 EDT 2020. Contains 335676 sequences. (Running on oeis4.)