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A027375
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Number of aperiodic binary strings of length n; also number of binary sequences with primitive period n.
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85
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0, 2, 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, 4294901760
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OFFSET
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0,2
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COMMENTS
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A sequence S is aperiodic if it is not of the form S = T^k with k>1. - N. J. A. Sloane, Oct 26 2012
Equivalently, number of output sequences with primitive period n from a simple cycling shift register. - Frank Ruskey, Jan 17 2000
Also, the number of nonempty subsets A of the set of the integers 1 to n such that gcd(A) is relatively prime to n (for n>1). - R. J. Mathar, Aug 13 2006; range corrected by Geoffrey Critzer, Dec 07 2014
Without the first term, this sequence is the Moebius transform of 2^n (n>0). For n > 0, a(n) is also the number of periodic points of period n of the transform associated to the Kolakoski sequence A000002. This transform changes a sequence of 1's and 2's by the sequence of the lengths of its runs. The Kolakoski sequence is one of the two fixed points of this transform, the other being the same sequence without the initial term. A025142 and A025143 are the 2 periodic points of period 2. A001037(n) = a(n)/n gives the number of orbits of size n. - Jean-Christophe Hervé, Oct 25 2014
There are 2^n strings of length n that can be formed from the symbols 0 and 1; in the example below with a(3) = 6, the last two strings that are not aperiodic binary strings are { 000, 111 }, corresponding to 0^3 and 1^3, using the notation of the first comment.
Two properties mentioned by Krusemeyer et al. are:
1) For any n > 2, a(n) is divisible by 6.
2) Lim_{n->oo} a(n+1)/a(n) = 2. (End)
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REFERENCES
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J.-P. Allouche and J. Shallit, Automatic Sequences, Cambridge Univ. Press, 2003, p. 13. - From N. J. A. Sloane, Oct 26 2012
E. R. Berlekamp, Algebraic Coding Theory, McGraw-Hill, NY, 1968, p. 84.
Blanchet-Sadri, Francine. Algorithmic combinatorics on partial words. Chapman & Hall/CRC, Boca Raton, FL, 2008. ii+385 pp. ISBN: 978-1-4200-6092-8; 1-4200-6092-9 MR2384993 (2009f:68142). See p. 164.
S. W. Golomb, Shift-Register Sequences, Holden-Day, San Francisco, 1967.
Mark I. Krusemeyer, George T. Gilbert, Loren C. Larson, A Mathematical Orchard, Problems and Solutions, MAA, 2012, Problem 128, pp. 225-227.
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LINKS
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J.-P. Allouche, Note on the transcendence of a generating function. In A. Laurincikas and E. Manstavicius, editors, Proceedings of the Palanga Conference for the 75th birthday of Prof. Kubilius, New trends in Probab. and Statist., Vol. 4, pages 461-465, 1997.
Guilhem Gamard, Gwenaël Richomme, Jeffrey Shallit and Taylor J. Smith, Periodicity in rectangular arrays, arXiv:1602.06915 [cs.DM], 2016; Information Processing Letters 118 (2017) 58-63. See Table 1.
Robert M. May, Simple mathematical models with very complicated dynamics, Nature, Vol. 261, June 10, 1976, pp. 459-467; reprinted in The Theory of Chaotic Attractors, pp. 85-93. Springer, New York, NY, 2004. The sequences listed in Table 2 are A000079, A027375, A000031, A001037, A000048, A051841. - N. J. A. Sloane, Mar 17 2019
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FORMULA
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a(n) = Sum_{d|n} mu(d)*2^(n/d).
Sum_{d|n} a(n) = 2^n.
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EXAMPLE
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a(3) = 6 = |{ 001, 010, 011, 100, 101, 110 }|. - corrected by Geoffrey Critzer, Dec 07 2014
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MAPLE
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MATHEMATICA
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Table[ Apply[ Plus, MoebiusMu[ n / Divisors[n] ]*2^Divisors[n] ], {n, 1, 32} ]
a[0]=0; a[n_] := DivisorSum[n, MoebiusMu[n/#]*2^#&]; Array[a, 40, 0] (* Jean-François Alcover, Dec 01 2015 *)
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PROG
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(PARI) a(n) = sumdiv(n, d, moebius(n\d)*2^d);
(Python)
from sympy import mobius, divisors
def a(n): return sum(mobius(d)*2**(n//d) for d in divisors(n))
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CROSSREFS
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A038199 and A056267 are essentially the same sequence with different initial terms.
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KEYWORD
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nonn,nice,easy
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AUTHOR
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STATUS
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approved
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