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%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
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