a(n) = n if n odd, n/2 if n even.

Terms

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