

A307247


Second digit in the expansion of n in Fraenkel's exotic ternary representation.


1



0, 0, 0, 1, 1, 1, 2, 0, 0, 0, 1, 1, 1, 2, 0, 0, 0, 0, 0, 0, 1, 1, 1, 2, 0, 0, 0, 1, 1, 1, 2, 0, 0, 0, 0, 0, 0, 1, 1, 1, 2, 0, 0, 0, 1, 1, 1, 2, 0, 0, 0, 1, 1, 1, 2, 0, 0, 0, 0, 0, 0, 1, 1, 1, 2, 0, 0, 0, 1, 1, 1, 2, 0, 0, 0, 0, 0, 0, 1, 1, 1, 2, 0, 0, 0, 1
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OFFSET

1,7


COMMENTS

Let {p_i, i >= 0} = {1,3,7,17,41,99,...} denote the numerators of successive convergents to sqrt(2) (see A001333). Then any n >= 0 has a unique representation as n = Sum_{i >= 0} d_i*p_i, with 0 <= d_i <= 2, d_{i+1}=2 => d_i=0. Sequence gives a(n+1) = d_1.
Let x be the 3symbol Pell word A294180 = 1, 2, 3, 1, 2, 3, 1, 1, 2, 3, 1, 2, ... Let delta be the morphism
1 > 000, 2 > 111, 3 > 2.
Then delta(x) = (a(n)). This can be proved by induction, starting from the knowledge that the sequence of first digits d_0 = d_0(n) of n in the exotic ternary expansion shifted by 1 is equal to x (see A263844).
More generally, the sequence of kth digits d_k shifted by 1 is equal to delta_k(x), where the morphism delta_k is given by
1 > U_k, 2 > V_k, 3 > W_k.
Here U_k is a concatenation of p_{k+1} letters 0, V_k is a concatenation of p_{k+1} letters 1, and W_k is a concatenation of p_k letters 2.


LINKS

Michel Dekking, Table of n, a(n) for n = 1..5000 (restored by Georg Fischer, Apr 05 2019)
F. Michel Dekking, Morphisms, Symbolic Sequences, and Their Standard Forms, Journal of Integer Sequences, Vol. 19 (2016), Article 16.1.1.
Aviezri S. Fraenkel, On the recurrence f(m+1)= b(m)*f(m)f(m1) and applications, Discrete Mathematics 224 (2000), pp. 273279.
A. S. Fraenkel, An exotic ternary representation of the first few positive integers (Table 2 from Fraenkel (2000).)


CROSSREFS

Cf. A263844, A001333.
Sequence in context: A330268 A089310 A129753 * A147693 A070936 A014081
Adjacent sequences: A307244 A307245 A307246 * A307248 A307249 A307250


KEYWORD

nonn


AUTHOR

Michel Dekking, Apr 01 2019


STATUS

approved



