%I #6 Jun 30 2012 09:29:30
%S 1,3,13,31,113,131,133,311,313,331,1113,1131,1133,1311,1331,1333,3111,
%T 3113,3133,3311,3313,3331,11113,11131,11133,11311,11313,11331,11333,
%U 13111,13113,13131,13133,13311,13313,13331,13333,31111,31113,31131,31133,31311,31313,31331,31333,33111,33113,33131,33133,33311,33313,33331
%N List of primitive words over the alphabet {1,3}.
%C A word w is primitive if it cannot be written as u^k with k>1; otherwise it is imprimitive.
%C The {0,1} version of this sequence is
%C 0, 1, 01, 10, 001, 010, 011, 100, 101, 110, 0001, 0010, 0011, 0100, 0110, 0111, 1000, 1001, 1011, 1100, 1101, 1110, 00001, 00010, 00011, 00100, 00101, 00110, 00111, 01000, 01001, 01010, 01011, 01100, 01101, 01110, 01111, 10000, 10001, 10010, 10011, 10100, 10101, 10110, 10111, 11000, 11001, 11010, 11011, 11100, 11101, 11110, ...,
%C but this cannot be included as a sequence in the OEIS since it contains nonzero "numbers" beginning with 0.
%D A. de Luca and S. Varricchio, Finiteness and Regularity in Semigroups and Formal Languages, Monographs in Theoretical Computer Science, Springer-Verlag, Berlin, 1999. See p. 10.
%Y Cf. A213969-A213974.
%K nonn,base
%O 1,2
%A _N. J. A. Sloane_, Jun 30 2012