a(n) = (1/2)*s(n), where s(n) is n-th even number in A002251.

Terms

a(0) =1a(1) =5a(2) =2a(3) =3a(4) =9a(5) =10a(6) =4a(7) =13a(8) =14a(9) =6a(10) =17a(11) =18a(12) =7a(13) =8a(14) =22a(15) =26a(16) =27a(17) =11a(18) =30a(19) =31a(20) =12a(21) =34a(22) =35a(23) =39a(24) =15a(25) =16a(26) =43a(27) =47a(28) =48a(29) =19