Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #30 Mar 31 2024 12:04:38
%S 0,0,0,6,24,78,186,372,876,1632,3024,5310,8496,13344,21186,31878,
%T 46752,66936,94800,130194
%N 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").
%C 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.
%H Fred Lunnon, <a href="/A180437/a180437.txt">Magma program</a>
%o (Magma) // See Links.
%Y Cf. A005598, A180238, A180239, A180438, A180439.
%K nonn,more
%O 0,4
%A _Fred Lunnon_, Sep 05 2010