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A060032 Fixed point of the morphism 1 -> 121, 2 -> 122, starting from 1. 4
1, 121, 121122121, 121122121121122122121122121, 121122121121122122121122121121122121121122122121122122121122121121122122121122121 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,2
COMMENTS
Previous name was: Ana sequence.
Let A(n), N(n) denote the number of 1's and the number of 2's in a(n). Then A(n) = (3^(k-1) + 1)/2, N(n) = (3^(k-1) - 1)/2. Hence lim_{n} A(n)/N(n) = 1.
In "Wonders of Numbers", Pickover considers a "fractal bar code" constructed from the Ana sequence. Start with a segment I of fixed length; at stage n, evenly subdivide I into as many non-overlapping closed intervals as there are letters in the n-th term of the Ana sequence; then shade the intervals corresponding to a's. It can be shown that a fractal set defined from this construction has fractal dimension = 1.
Fixed point of the morphism 1 -> 121, 2 -> 122, starting from a(1) = 1. See A060236. - Robert G. Wilson v, Mar 05 2005
REFERENCES
C. Pickover, Wonders of Numbers, Chap. 69 "An A?", Oxford University Press, NY, 2001, p. 167-171.
LINKS
Joseph L. Pe, Ana's Golden Fractal, Fractals, Vol. 11, No. 4 (2003) 309-313.
C. A. Pickover, "Wonders of Numbers, Adventures in Mathematics, Mind and Meaning," Zentralblatt review
FORMULA
Begin with the letter "a". Generate next term by using the indefinite article as appropriate, e.g., "an a", then "an a, an n, an a" etc. Assign a=1, n=2.
EXAMPLE
a(2) = ana = 121, a(3) = ana ann ana = 121122121.
MATHEMATICA
f[n_] := FromDigits[ Nest[ Flatten[ # /. {1 -> {1, 2, 1}, 2 -> {1, 2, 2}}] &, {1}, n]]; Table[ f[n], {n, 0, 4}] (* Robert G. Wilson v, Mar 05 2005 *)
CROSSREFS
Cf. A060236.
Sequence in context: A068121 A013859 A303897 * A109643 A080826 A043646
KEYWORD
nonn
AUTHOR
Jason Earls, Mar 17 2001
EXTENSIONS
Additional comments from Joseph L. Pe, Mar 11 2002
More descriptive name from comment, Joerg Arndt, Jan 23 2024
STATUS
approved

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Last modified March 19 01:57 EDT 2024. Contains 370952 sequences. (Running on oeis4.)