1, 3 and the positive even numbers.

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =6a(5) =8a(6) =10a(7) =12a(8) =14a(9) =16a(10) =18a(11) =20a(12) =22a(13) =24a(14) =26a(15) =28a(16) =30a(17) =32a(18) =34a(19) =36a(20) =38a(21) =40a(22) =42a(23) =44a(24) =46a(25) =48a(26) =50a(27) =52a(28) =54a(29) =56