A squarefree (or Thue-Morse) ternary sequence: closed under a->abc, b->ac, c->b.

Terms

a(0) =2a(1) =1a(2) =3a(3) =2a(4) =3a(5) =1a(6) =2a(7) =1a(8) =3a(9) =1a(10) =2a(11) =3a(12) =2a(13) =1a(14) =3a(15) =2a(16) =3a(17) =1a(18) =2a(19) =3a(20) =2a(21) =1a(22) =3a(23) =1a(24) =2a(25) =1a(26) =3a(27) =2a(28) =3a(29) =1