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

 

Logo

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!)
A242951 Number of ternary squarefree words x of length n for which some self-shuffle of x is also squarefree. 0
0, 0, 6, 6, 12, 18, 30, 42, 36, 54, 138, 168, 234 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

"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].

LINKS

Table of n, a(n) for n=1..13.

T. Harju and M. Mueller, Square-free shuffles of words, arxiv preprint, 2013, Table 3, page 7.

CROSSREFS

Cf. A242949.

Sequence in context: A315794 A315795 A315796 * A022089 A275288 A110357

Adjacent sequences:  A242948 A242949 A242950 * A242952 A242953 A242954

KEYWORD

nonn,more

AUTHOR

Jeffrey Shallit, May 27 2014

STATUS

approved

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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 24 20:34 EST 2020. Contains 338616 sequences. (Running on oeis4.)