A291799 - OEIS

%I #9 Sep 08 2017 16:06:30

%S 0,2,0,2,6,6,0,0,0,6,6,6,6,6,0,6,0,6,6,2,6,6,6,6,6,6,4,6,0,6,0,6,6,4,

%T 0,0,6,6,6,0,0,0,6,0,6,6,4,6,0,6,6,0,6,0,6,6,0,6,6,6,10,0,0,0,6,6,4,6,

%U 6,6,0,4,0,0,0,6,6,6,0,6,4,6,6,2,6,6,6

%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) = period of orbit of that word, or 0 if the orbit ends at the empty word.

%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 A291793 (or A284121) for the words in A291797.

%H Lars Blomberg, <a href="/A291799/b291799.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, A284121, A291793, A291797.

%K nonn

%O 1,2

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

%E a(31)-a(87) from _Lars Blomberg_, Sep 08 2017