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A056267 Number of primitive (aperiodic) words of length n which contain exactly two different symbols. 4
0, 2, 6, 12, 30, 54, 126, 240, 504, 990, 2046, 4020, 8190, 16254, 32730, 65280, 131070, 261576, 524286, 1047540, 2097018, 4192254, 8388606, 16772880, 33554400, 67100670, 134217216, 268419060, 536870910, 1073708010, 2147483646 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

REFERENCES

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

LINKS

Table of n, a(n) for n=1..31.

FORMULA

a(n) = Sum_{d|n} mu(d)*A000918(n/d), n>0.

PROG

(PARI) a(n) = sumdiv(n, d, moebius(d)*(2^(n/d) - 2)); \\ Michel Marcus, Jun 30 2019

CROSSREFS

Cf. A000079, A000918.

A027375 and A038199 are essentially the same sequence with different initial terms.

Sequence in context: A224532 A179674 A038199 * A133996 A284573 A080742

Adjacent sequences:  A056264 A056265 A056266 * A056268 A056269 A056270

KEYWORD

nonn

AUTHOR

Marks R. Nester

EXTENSIONS

Corrected and extended by Franklin T. Adams-Watters and T. D. Noe, Oct 25 2006

STATUS

approved

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Last modified July 13 08:26 EDT 2020. Contains 335685 sequences. (Running on oeis4.)