If n even, then 2n. If n odd, then nearest integer to 2n/3.

Terms

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