A291800 - OEIS

%I #9 Sep 08 2017 16:07:13

%S 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,

%T 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,

%U 17,0,13,19,0,17,19,19,31,0,0,0,15,13,13,19,13,19,0

%N 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.

%C 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.

%C 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.

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

%H Lars Blomberg, <a href="/A291800/b291800.txt">Table of n, a(n) for n = 1..8190</a> (For terms in A291797 up to length 36.)

%H Peter R. J. Asveld, <a href="http://doc.utwente.nl/66184/1/1988m20.pdf">On a Post's System of Tag</a>. Bulletin of the EATCS 36 (1988), 96-102. See Table 3.

%Y Cf. A284116, A291794, A291797.

%K nonn

%O 1,2

%A _N. J. A. Sloane_, Sep 04 2017

%E a(31)-a(71) from _Lars Blomberg_, Sep 08 2017