[seqfan] A007489 and strings containing all permutations

[Jason Orendorff]

I think A007489 gives the length of the shortest string of n symbols that
contains all n! permutations of those n symbols as contiguous substrings.  The
first 4 such strings are: 1, 121, 123121321, 123412314231243121342132413214321,
having lengths 1, 3, 9, 33. Neat, huh? It seems interesting enough to go in the
entry, if it's true. I think it is; a summary of my argument is posted here:

  http://bit.ly/9h917c

Unfortunately, I can't find a reference for this. All the papers I've
been able to
find are about a different problem, described here:

  http://garden.irmacs.sfu.ca/?q=op/smallest_universal_supersequence

Surely this is known. Can anyone provide the reference?

Thanks for your time.

-- 
Jason Orendorff