OFFSET
0,3
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. Computation: Fred Lunnon for 0 <= n <= 19 (Magma). The program in A180437 counts k-special words for k = 1, ..., m, where m = 3 denotes the size of the alphabet.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Fred Lunnon, Sep 05 2010
STATUS
approved