OFFSET
1,2
COMMENTS
Also called Zimin words.
a(n) is a palindrome for n<10; it is debatable whether a(n) can be called a Zimin word for n>=10 (see the Comments in A018238). - Danny Rorabaugh, Sep 26 2015
LINKS
J. Cooper and D. Rorabaugh, Bounds on Zimin Word Avoidance, arXiv:1409.3080 [math.CO], 2014; Congressus Numerantium, 222 (2014), 87-95.
L. J. Cummings and M. Mays, A one-sided Zimin construction, Electron. J. Combin. 8 (2001), #R27.
A. I. Zimin, Blocking sets of terms, Math. USSR Sbornik, 47 (1984), No. 2, 353-364.
FORMULA
The Zimin words are defined here by Z_1 = 1, Z_n = Z_{n-1}nZ_{n-1}. - Dmitry Kamenetsky, Sep 30 2006
MATHEMATICA
a = {1}; Do[w = IntegerDigits@ a[[n - 1]]; AppendTo[a, FromDigits@ Join[w, IntegerDigits@ n, w]], {n, 2, 7}]; a (* Michael De Vlieger, Sep 26 2015 *)
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Apr 08 2003
EXTENSIONS
More terms from Joshua Zucker, May 08 2006
"Palindromes" replaced with "Numbers" in sequence name by Danny Rorabaugh, Sep 26 2015
Shorter name by Joerg Arndt, Aug 28 2021
STATUS
approved