a(n) is the smallest number not of the form a(i) (1<=i<=n-1) or a(i)+a(n-1) (1<=i<=n-2).

Terms

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