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A180437 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"). 3
0, 0, 0, 6, 24, 78, 186, 372, 876, 1632, 3024, 5310, 8496, 13344, 21186, 31878, 46752, 66936, 94800, 130194 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

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.

LINKS

Table of n, a(n) for n=0..19.

Fred Lunnon, Magma program

PROG

(Magma) (see Links)

CROSSREFS

Cf. A005598, A180238, A180239, A180438, A180439.

Sequence in context: A257956 A341364 A080373 * A276179 A162583 A259662

Adjacent sequences:  A180434 A180435 A180436 * A180438 A180439 A180440

KEYWORD

nonn,more

AUTHOR

Fred Lunnon, Sep 05 2010

STATUS

approved

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Last modified August 15 02:47 EDT 2022. Contains 356122 sequences. (Running on oeis4.)