a(n) = t(5n), where t = A001285 (Thue-Morse sequence).

Terms

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