0, 2, 4 and the odd numbers.

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =4a(5) =5a(6) =7a(7) =9a(8) =11a(9) =13a(10) =15a(11) =17a(12) =19a(13) =21a(14) =23a(15) =25a(16) =27a(17) =29a(18) =31a(19) =33a(20) =35a(21) =37a(22) =39a(23) =41a(24) =43a(25) =45a(26) =47a(27) =49a(28) =51a(29) =53