Skip 1, take 1, skip 2, take 2, skip 3, take 3, etc.

Terms

a(0) =2a(1) =5a(2) =6a(3) =10a(4) =11a(5) =12a(6) =17a(7) =18a(8) =19a(9) =20a(10) =26a(11) =27a(12) =28a(13) =29a(14) =30a(15) =37a(16) =38a(17) =39a(18) =40a(19) =41a(20) =42a(21) =50a(22) =51a(23) =52a(24) =53a(25) =54a(26) =55a(27) =56a(28) =65a(29) =66