a(n) = t(1+3n), where t = A001285 (Thue-Morse sequence).

Terms

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