A291800 Take n-th word over {1,2} listed in A291797 and apply the Post tag system described in A284116 (but adapted to the alphabet {1,2}); a(n) = length of first word we see in the orbit of that word that is in the cycle, if the orbit cycles, or 0 if the orbit reaches the empty string, or -1 if the orbit is unbounded.

0, 5, 0, 6, 15, 15, 0, 0, 0, 15, 15, 15, 15, 15, 0, 15, 0, 15, 15, 12, 15, 15, 15, 15, 19, 19, 13, 15, 0, 19, 0, 15, 15, 13, 0, 0, 15, 15, 15, 0, 0, 0, 13, 0, 19, 19, 13, 14, 0, 19, 19, 0, 17, 0, 13, 19, 0, 17, 19, 19, 31, 0, 0, 0, 15, 13, 13, 19, 13, 19, 0

Offset: 1

Author

N. J. A. Sloane, Sep 04 2017

Keywords

• nonn

Comments

Post's tag system maps a word w over {1,2} to w', where if w begins with 1, w' is obtained by appending 11 to w and deleting the first three letters, or if w begins with 2, w' is obtained by appending 2212 to w and deleting the first three letters.

We work over {1,2} rather than the official alphabet {0,1} because of the prohibition in the OEIS of terms (other than 0 itself) which begin with 0.

This is an analog of A291794 for the words in A291797.

Links

• Lars Blomberg, Table of n, a(n) for n = 1..8190 (For terms in A291797 up to length 36.)
• Peter R. J. Asveld, On a Post's System of Tag. Bulletin of the EATCS 36 (1988), 96-102. See Table 3.

Crossrefs

Cf. A284116, A291794, A291797.

Extensions

a(31)-a(71) from Lars Blomberg, Sep 08 2017