%I
%S 0,0,6,12,30,24,42,78,138,228,396,168,1008
%N Number of distinct ternary squarefree words of length 2n that can be obtained as the selfshuffle of a ternary squarefree word of length n.
%C "squarefree" means it contains no block of the form xx, with x nonempty. A length2n word w is in the selfshuffle of a lengthn word x if there is a disjoint partition of the indices {1,2,..., 2n} into two increasing sequences of length n, say s and t, such that x = w[s] = w[t].
%H T. Harju and M. Mueller, <a href="http://arxiv.org/abs/1309.2137">Squarefree shuffles of words</a>, arxiv preprint, 2013, Table 3, page 7.
%e a(3) = 6, as the sequences are 010212 (arising from selfshuffle of 012), and the 5 others arising from permutation of the letters 0, 1, 2.
%K nonn,more
%O 1,3
%A _Jeffrey Shallit_, May 27 2014
