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Search: id:A001285
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| A001285 |
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Thue-Morse sequence: let A_k denote the first 2^k terms; then A_0 = 1 and for k >= 0, A_{k+1} = A_k B_k, where B_k is obtained from A_k by interchanging 1's and 2's.
(Formerly M0193 N0071)
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+0
45
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| 1, 2, 2, 1, 2, 1, 1, 2, 2, 1, 1, 2, 1, 2, 2, 1, 2, 1, 1, 2, 1, 2, 2, 1, 1, 2, 2, 1, 2, 1, 1, 2, 2, 1, 1, 2, 1, 2, 2, 1, 1, 2, 2, 1, 2, 1, 1, 2, 1, 2, 2, 1, 2, 1, 1, 2, 2, 1, 1, 2, 1, 2, 2, 1, 2, 1, 1, 2, 1, 2, 2, 1, 1, 2, 2, 1, 2, 1, 1, 2, 1, 2, 2, 1, 2, 1, 1, 2, 2, 1, 1, 2, 1, 2, 2, 1, 1, 2, 2, 1, 2, 1
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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Or, follow a(0), .., a(2^k-1) by its complement.
Equals convergent as an infinite string of A161175 row terms. [From Gary W. Adamson (qntmpkt(AT)yahoo.com), Jun 05 2009]
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REFERENCES
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J.-P. Allouche and J. Shallit, Automatic Sequences, Cambridge Univ. Press, 2003, p. 15.
F. Axel et al., Vibrational modes in a one dimensional "quasi-alloy": the Morse case, J. de Physique, Colloq. C3, Supp. to No. 7, Vol. 47 (Jul 1986), pp. C3-181-C3-186; see Eq. (10).
F. Dejean, Sur un theoreme de Thue. J. Combinatorial Theory Ser. A 13 (1972), 90-99.
G. Everest, A. van der Poorten, I. Shparlinski and T. Ward, Recurrence Sequences, Amer. Math. Soc., 2003; see esp. p. 255.
W. H. Gottschalk and G. A. Hedlund, Topological Dynamics. American Mathematical Society, Colloquium Publications, Vol. 36, Providence, RI, 1955, p. 105.
G. A. Hedlund, Remarks on the work of Axel Thue on sequences, Nordisk Mat. Tid., 15 (1967), 148-150.
A. Hof, O. Knill and B. Simon, Singular continuous spectrum for palindromic Schroedinger operators, Commun. Math. Phys. 174 (1995), 149-159.
M. Lothaire, Combinatorics on Words. Addison-Wesley, Reading, MA, 1983, p. 23.
M. Morse, Recurrent geodesics on a surface of negative curvature, Trans. Amer. Math. Soc., 22 (1921), 84-100.
A. Salomaa, Jewels of Formal Language Theory. Computer Science Press, Rockville, MD, 1981, p. 6.
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LINKS
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T. D. Noe, Table of n, a(n) for n = 0..1023
J.-P. Allouche and J. O. Shallit, The Ubiquitous Prouhet-Thue-Morse Sequence, in C. Ding. T. Helleseth and H. Niederreiter, eds., Sequences and Their Applications: Proceedings of SETA '98, Springer-Verlag, 1999, pp. 1-16.
Michael Gilleland, Some Self-Similar Integer Sequences
S. Wolfram, Source for short Thue-Morse generating code
Index entries for "core" sequences
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FORMULA
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a(2n)=a(n), a(2n+1)=3-a(n), a(0)=1. Also, a(k+2^m)=3-a(k) if 0<=k<2^m.
a(n) = 2-A010059(n) = 1/2*(3-(-1)^A000120(n)). - Ralf Stephan (ralf(AT)ark.in-berlin.de), Jun 20 2003
a(n)=sum(k=0, n, binomial(n, k){mod 2}) {mod 3}=A001316(n) {mod 3} - Benoit Cloitre (benoit7848c(AT)orange.fr), May 09 2004
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MAPLE
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A001285 := proc(n) option remember; if n=0 then 1 elif n mod 2 = 0 then A001285(n/2) else 3-A001285((n-1)/2); fi; end;
s := proc(k) local i, ans; ans := [ 1, 2 ]; for i from 0 to k do ans := [ op(ans), op(map(n->if n=1 then 2 else 1 fi, ans)) ] od; RETURN(ans); end; t1 := s(6); A001285 := n->t1[n]; # s(k) gives first 2^(k+2) terms
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MATHEMATICA
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Nest[ Function[l, {Flatten[(l /. {2 -> {2, 1}, 1 -> {1, 2}})]}], {1}, 7] (from Robert G. Wilson v Feb 26 2005)
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PROGRAM
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(PARI) a(n)=1+subst(Pol(binary(n)), x, 1)%2
(PARI) a(n)=sum(k=0, n, binomial(n, k)%2)%3
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CROSSREFS
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Cf. A010060 (for 0, 1 version), A003159. A001285(n)=1+A010060(n).
A026465 gives run lengths.
Cf. A010059 (1, 0 version).
A161175 [From Gary W. Adamson (qntmpkt(AT)yahoo.com), Jun 05 2009]
Adjacent sequences: A001282 A001283 A001284 this_sequence A001286 A001287 A001288
Sequence in context: A035214 A071292 A088569 this_sequence A088424 A097456 A087775
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KEYWORD
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nonn,easy,core,nice
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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