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A180437
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a(n) counts the distinct cubical (on alphabet of 3 symbols) billiard words with length n, acting as prefix to just k = 1 such word of length n+1 (that is, not "special").
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3
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0, 0, 0, 6, 24, 78, 186, 372, 876, 1632, 3024, 5310, 8496, 13344, 21186, 31878, 46752, 66936, 94800, 130194
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OFFSET
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0,4
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COMMENTS
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By symmetry under reversal, a(n) also counts length n cubical billiard words acting as suffix to just k length n+1 cubical billiard words. The attached program counts k-special words for k = 1,...,m, where m = 3 denotes the size of the alphabet.
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LINKS
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Table of n, a(n) for n=0..19.
Fred Lunnon, Magma program
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PROG
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(Magma) (see Links)
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CROSSREFS
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Cf. A005598, A180238, A180239, A180438, A180439.
Sequence in context: A257956 A341364 A080373 * A276179 A162583 A259662
Adjacent sequences: A180434 A180435 A180436 * A180438 A180439 A180440
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KEYWORD
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nonn,more
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AUTHOR
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Fred Lunnon, Sep 05 2010
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STATUS
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approved
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