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A092782
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The ternary tribonacci word; also a Rauzy fractal sequence: fixed point of the morphism 1 -> 12, 2 -> 13, 3 -> 1, starting from a(1) = 1.
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41
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1, 2, 1, 3, 1, 2, 1, 1, 2, 1, 3, 1, 2, 1, 2, 1, 3, 1, 2, 1, 1, 2, 1, 3, 1, 2, 1, 3, 1, 2, 1, 1, 2, 1, 3, 1, 2, 1, 2, 1, 3, 1, 2, 1, 1, 2, 1, 3, 1, 2, 1, 1, 2, 1, 3, 1, 2, 1, 2, 1, 3, 1, 2, 1, 1, 2, 1, 3, 1, 2, 1, 3, 1, 2, 1, 1, 2, 1, 3, 1, 2, 1, 2, 1, 3, 1, 2, 1, 1, 2, 1, 3, 1, 2, 1, 2, 1, 3, 1, 2, 1, 1, 2, 1, 3
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OFFSET
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1,2
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COMMENTS
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See A080843 for the {0,1,2} version, which in a sense is the most basic version.
See also A103269 for another version with further references and comments.
Also called a tribonacci word. In the limit the ratios #1's : #2's : #3's are t^2 : t : 1 where t is the tribonacci constant 1.839286755... (A058265). - Frank M Jackson, Mar 29 2018
a(n)-1 is the number of trailing 0's in the maximal tribonacci representation of n (A352103). - Amiram Eldar, Feb 29 2024
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REFERENCES
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This entry has a fairly complete list of references and links concerning the ternary tribonacci word. - N. J. A. Sloane, Aug 17 2018
J.-P. Allouche and J. Shallit, Automatic Sequences, Cambridge Univ. Press, 2003, p. 246.
Michel Rigo, Formal Languages, Automata and Numeration Systems, 2 vols., Wiley, 2014. Mentions this sequence - see "List of Sequences" in Vol. 2.
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LINKS
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Pierre Arnoux and Edmund Harriss, What is a Rauzy Fractal?, Notices Amer. Math. Soc., 61 (No. 7, 2014), 768-770, also p. 704 and front cover.
Elena Barcucci, Luc Belanger and Srecko Brlek, On tribonacci sequences, Fib. Q., 42 (2004), 314-320. See T on page 315.
Aayush Rajasekaran, Narad Rampersad, and Jeffrey Shallit, Overpals, Underlaps, and Underpals, In: Brlek S., Dolce F., Reutenauer C., Vandomme É. (eds) Combinatorics on Words, WORDS 2017, Lecture Notes in Computer Science, vol 10432.
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FORMULA
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EXAMPLE
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The first few steps of the substitution are
Start: 1
Maps:
1 --> 12
2 --> 13
3 --> 1
-------------
0: (#=1)
1
1: (#=2)
12
2: (#=4)
1213
3: (#=7)
1213121
4: (#=13)
1213121121312
5: (#=24)
121312112131212131211213
6: (#=44)
12131211213121213121121312131211213121213121
7: (#=81)
121312112131212131211213121312112131212131211213121121312121312112131213121121312
(End)
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MAPLE
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f(1):= (1, 2): f(2):= (1, 3): f(3):= (1): A:= [1]:
for i from 1 to 16 do A:= map(f, A) od:
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MATHEMATICA
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Nest[ Flatten[# /. {1 -> {1, 2}, 2 -> {1, 3}, 3 -> 1}] &, {1}, 8] (* Robert G. Wilson v, Mar 04 2005 and updated Apr 29 2018 *)
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PROG
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(PARI) w=vector(9, x, []); w[1]=[1];
for(n=2, 9, for(k=1, #w[n-1], m=w[n-1][k]; v=[]; if(m-1, if(m-2, v=[1], v=[1, 3]), v=[1, 2]); w[n]=concat(w[n], v)));
(PARI)
strsub(s, vv, off=0)=
{
my( nl=#vv, r=[], ct=1 );
while ( ct <= #s,
r = concat(r, vv[ s[ct] + (1-off) ] );
ct += 1;
);
return( r );
}
t=[1]; for (k=1, 10, t=strsub( t, [[1, 2], [1, 3], [1]], 1 ) ); t
(PARI) A092782_vec(N, s=[[1, 2], [1, 3], 1], A=[1])={while(#A<N, A=concat(vecextract(s, A))); A} \\ Return at least N terms. - M. F. Hasler, Dec 14 2018
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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