If n is odd then n, otherwise 2n.

Terms

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