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A080846 Fixed point of the morphism 0->010, 1->011, starting from a(1) = 0. 9
0, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1, 0, 0, 1, 1, 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1, 0, 0, 1, 1, 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1, 0, 0, 1, 1, 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1, 0, 0, 1, 1, 0, 1, 1, 0, 1, 0, 0, 1, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

A cube-free word.

A generalized choral sequence c(3n+r_0)=0, c(3n+r_1)=1, c(3n+r_c)=c(n), with r_0=0, r_1=1, and r_c=2. [From Joel Reyes Noche (joel.noche(AT)up.edu.ph), Jul 09 2009]

From Joerg Arndt, Apr 15 2010: (Start)

Turns (by 120 degrees) of the terdragon curve which can be rendered as follows:

  [Init] Set n=0 and direction=0.

  [Draw] Draw a unit line (in the current direction). Turn left/right if a(n) is zero/nonzero respectively.

  [Next] Set n=n+1 and goto (draw).

See fxtbook link below. (End)

REFERENCES

J. Berstel and J. Karhumaki, Combinatorics on words - a tutorial, Bull. EATCS, #79 (2003), pp. 178-228.

J. R. Noche, Generalized Choral Sequences, Matimyas Matematika, 31(2008), 25-28. [From Joel Reyes Noche (joel.noche(AT)up.edu.ph), Jul 09 2009]

LINKS

Table of n, a(n) for n=0..104.

Joerg Arndt Matters Computational (The Fxtbook), section 1.31.4, pp. 92-95; dragon curve picture on p. 93.

Jean Berstel, Home Page

Dimitri Hendriks, Frits G. W. Dannenberg, Jorg Endrullis, Mark Dow and Jan Willem Klop, Arithmetic Self-Similarity of Infinite Sequences, arXiv preprint 1201.3786, 2012.

FORMULA

a(n) = (A062756(n) - A062756(n+1) + 1)/2, where A062756(n) is the number of 1's in the ternary expansion of n. From formula in A062756: G.f.: A(x) = 1/(1-x)/2 - Sum_{k>=0} x^(3^k-1)/(1+x^(3^k)+x^(2*3^k))/2. - Paul D. Hanna, Feb 24 2006

Given G.f. A(x) then B(x) = x * A(x) satisfies B(x) = x^2 / (1 - x^3) + B(x^3). - Michael Somos, Jul 29 2009

a(3*n) = 0, a(3*n + 1) = 1, a(3*n - 1) = a(n - 1). - Michael Somos, Jul 29 2009

a(n) = -1 + A060236(n). [Joerg Arndt, Jan 21 2013]

EXAMPLE

Start: 0

Rules:

  0 --> 010

  1 --> 011

-------------

0:   (#=1)

  0

1:   (#=3)

  010

2:   (#=9)

  010011010

3:   (#=27)

  010011010010011011010011010

4:   (#=81)

  010011010010011011010011010010011010010011011010011011010011010010011011010011010

MAPLE

a:= proc(n) option remember;

      local m, r;

      r:= irem (n, 3, 'm');

      `if` (r<2, r, a(m))

    end:

seq (a(n), n=0..1000);

MATHEMATICA

Nest[Flatten[ # /. {0 -> {0, 1, 0}, 1 -> {0, 1, 1}}] &, {0}, 5]

PROG

(PARI) {a(n)=if(n<1, 0, polcoeff(1/(1-x)/2-sum(k=0, ceil(log(n+1)/log(3)), x^(3^k-1)/(1+x^(3^k)+x^(2*3^k)+x*O(x^n)))/2, n))} - Paul D. Hanna, Feb 24 2006

(PARI) {a(n) = if( n<1, 0, n++; n / 3^valuation(n, 3) % 3 -1 )} /* Michael Somos, Jul 29 2009 */

(C++) /* CAT algorithm */

bool bit_dragon3_turn(ulong &x)

/* Increment the radix-3 word x and return whether

   the number of ones in x is decreased. */

{

    ulong s = 0;

    while ( (x & 3) == 2 ) { x >>= 2; ++s; } /* scan over nines */

    bool tr = ( (x & 3) != 0 ); /* incremented word will have one less 1 */

    ++x; /* increment next digit */

    x <<= (s<<1); /* shift back */

    return tr;

} /* From Joerg Arndt, Apr 15 2010 */

CROSSREFS

See A060236 for another version.

Cf. A062756, A189628.

Sequence in context: A059651 A176405 A084091 * A082401 A157238 A059448

Adjacent sequences:  A080843 A080844 A080845 * A080847 A080848 A080849

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, Mar 29 2003

EXTENSIONS

More terms from Wouter Meeussen, Apr 01 2003

STATUS

approved

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Last modified November 28 01:41 EST 2014. Contains 250286 sequences.