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Search: id:A006156
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| A006156 |
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Number of ternary square-free words of length n.
(Formerly M2550)
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+0
6
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| 1, 3, 6, 12, 18, 30, 42, 60, 78, 108, 144, 204, 264, 342, 456, 618, 798, 1044, 1392, 1830, 2388, 3180, 4146, 5418, 7032, 9198, 11892, 15486, 20220, 26424, 34422, 44862, 58446, 76122, 99276, 129516, 168546, 219516, 285750
(list; graph; listen)
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OFFSET
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0,2
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REFERENCES
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F.-J. Brandenburg, Uniformly growing k-th power-free homomorphisms, Theoretical Computer Sci., 23 (1983), 69-82.
J. Brinkhuis, Non-repetitive sequences on three symbols, Quart. J. Math. Oxford, 34 (1983), 145-149.
John Noonan and Doron Zeilberger, The Goulden-Jackson Cluster Method: Extensions, Applications and Implementations, 1997.
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LINKS
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M. Baake, V. Elser and U. Grimm, Entropy of Square-Free Words
D. Ekhad and D. Zeilberger, There are more than 2^(n/17) n-letter ternary square-free words, J. Integer Sequences, vol. 1, 98.1.9
U. Grimm, Improved bounds on the number of ternary square-free word, J. Integer Sequences, vol. 4, 01.2.7
J. Noonan and D. Zeilberger, The Goulden-Jackson Cluster Method: Extensions, Applications and Implementations
C. Richard and U. Grimm, On the entropy and letter frequencies of ternary square-free words
Yuriy Tarannikov, The minimal density of a letter in an infinite ..., Journal of Integer Sequences, Vol. 5 (2002), Article 02.2.2
Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.
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CROSSREFS
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Cf. A060688.
Sequence in context: A028882 A024513 A116958 this_sequence A061776 A074899 A125851
Adjacent sequences: A006153 A006154 A006155 this_sequence A006157 A006158 A006159
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KEYWORD
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nonn,nice
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AUTHOR
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njas, Jeffrey Shallit, zeilberg(AT)euclid.math.temple.edu (Doron Zeilberger)
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