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Search: id:A008351
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| A008351 |
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Concatenate a(n-1) and a(n-2). |
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+0
4
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| 1, 2, 21, 212, 21221, 21221212, 2122121221221, 212212122122121221212, 2122121221221212212122122121221221, 2122121221221212212122122121221221212212122122121221212
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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A "non-commutative Fibonacci" sequence. Often written as: a, b, ba, bab, babba, babbabab, babbababbabba, babbababbabbababbabab, ...
Converges in the appropriate topology. - Dylan Thurston, Jan 28 2005
Do a web search on babbababbabbababbabab to get further links.
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REFERENCES
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D. E. Knuth, "The Art of Programming", Volume 1, "Fundamental Algorithms", third edition, problem 36 on page 86.
K. B. Stolarsky, Canadian Math. Bull. 19 (1976) pp. 473-482.
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LINKS
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Wikipedia, Lindenmayer system
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MATHEMATICA
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a[1] = 1; a[2] = 2; a[n_] := 10^Floor[ Log[10, a[n - 2]] +1]*a[n - 1] + a[n - 2] (from Robert G. Wilson v (rgwv(at)rgwv.com), Jan 26 2006)
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CROSSREFS
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See A008352 for another version.
Cf. A014675: 1->2, 2->21.
Sequence in context: A037495 A024763 A037575 this_sequence A037743 A037638 A131698
Adjacent sequences: A008348 A008349 A008350 this_sequence A008352 A008353 A008354
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KEYWORD
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nonn,base
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AUTHOR
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njas and J. H. Conway (conway(AT)math.princeton.edu)
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