A180437 - OEIS

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").

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: A225383 A257956 A341364 * A276179 A162583 A259662

Adjacent sequences: A180434 A180435 A180436 * A180438 A180439 A180440

KEYWORD

nonn,more

AUTHOR

Fred Lunnon, Sep 05 2010

STATUS

approved