The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Please make a donation to keep the OEIS running. We are now in our 56th year. In the past year we added 10000 new sequences and reached almost 9000 citations (which often say "discovered thanks to the OEIS"). Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A242949 Number of distinct ternary squarefree words of length 2n that can be obtained as the self-shuffle of a ternary squarefree word of length n. 1

%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 self-shuffle of a ternary squarefree word of length n.

%C "squarefree" means it contains no block of the form xx, with x nonempty. A length-2n word w is in the self-shuffle of a length-n 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">Square-free shuffles of words</a>, arxiv preprint, 2013, Table 3, page 7.

%e a(3) = 6, as the sequences are 010212 (arising from self-shuffle 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 4 02:18 EST 2020. Contains 338921 sequences. (Running on oeis4.)