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A131989
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Start with the symbol **|* and for each iteration replace * with **|*. This sequence is the number of *'s between each dash.
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1
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2, 3, 1, 2, 3, 3, 1, 2, 1, 2, 3, 1, 2, 3, 3, 1, 2, 3, 3, 1, 2, 1, 2, 3, 1, 2, 1, 2, 3, 1, 2, 3, 3, 1, 2, 1, 2, 3, 1, 2, 3, 3, 1, 2, 3, 3, 1, 2, 1, 2, 3, 1, 2, 3, 3, 1, 2, 3, 3, 1, 2, 1, 2, 3, 1, 2, 1, 2, 3, 1, 2, 3, 3, 1, 2, 1, 2, 3, 1, 2, 1, 2, 3, 1, 2, 3, 3, 1, 2, 1, 2, 3, 1, 2, 3, 3, 1, 2, 3
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OFFSET
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1,1
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COMMENTS
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If the leading a(1)=2 is dropped, at least the next 90 terms coincide with those of A026181. - R. J. Mathar, Jun 13 2008
Coding * by 1 and | by 2, the procedure is the same as performing the substitution sigma: 1 -> 1121, 2 -> 2. The return words of this morphism are 12, 112 and 1112. Under sigma these words transform as
12->11212, 112-> 112111212, 1112->1121112111212.
Coding the return words by their length minus one, the corresponding derivated morphism is
1-> 21, 2-> 231, 3-> 2331.
(a(n)) is the unique fixed point of this morphism.
(End)
a(n) = x(n+1), where x is the primitive Chacon sequence A049321 on the alphabet {3,1,2} instead of {0,1,2}. This follows from the fact that
sigma: 0->0012, 1->12, 2->012 and tau: 0->2001, 1->21, 2->201 are conjugated morphisms: tau(j) = 2 sigma(j) 2^{-1} for j=0,1,2. - Michel Dekking, Oct 23 2019
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LINKS
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FORMULA
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The following is a simple recursive method to generate this sequence. The sequence is lim_{ t -> oo } S_t, where S_0 = 1+, and S_{t+1} is obtained from the concatenation S_t S_t S_t by replacing the first + by the sum of the two numbers adjacent to it and deleting the second +.
Thus we have:
S_0 = 1+,
S_1 = 1+1+1+ -> 21+,
S_2 = 21+21+21+ -> 23121+,
S_3 = 23121+23121+23121+ -> 23123312123121+,
S_4 = 23123312123121+23123312123121+23123312123121+ -> 23123312123123312331212312123123312123121+, etc.
Denote the sequence by a(1), a(2), ...
Block t, that is, S_t omitting the final 1+, extends from n=1 through n=(3^t-1)/2.
Given n, to find a(n): first find t from
p = (3^(t-1)-1)/2 < n <= (3^t-1)/2.
Assume t >= 2. Then if n=(3^(t-1)+1)/2, a(n) = 3 and if n=3^(t-1), a(n) = 1.
Otherwise, a(n) = a(n'), where
n' = n-p if n<3^(t-1), otherwise n' = n-3^(t-1). (End)
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EXAMPLE
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The symbol through a few iterations: **|*, **|***|*|**|*, **|***|*|**|***|***|*|**|*|**|***|*|**|*, etc.
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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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Alex H. Bishop (AlexanderBishop(AT)stmarksschool.org), Oct 07 2007
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EXTENSIONS
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STATUS
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approved
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