a(n) = (1/2)*s(n), where s(n) is the n-th even number in A026255.

Terms

a(0) =1a(1) =2a(2) =3a(3) =7a(4) =4a(5) =8a(6) =9a(7) =5a(8) =6a(9) =13a(10) =14a(11) =15a(12) =10a(13) =20a(14) =11a(15) =21a(16) =22a(17) =12a(18) =26a(19) =27a(20) =28a(21) =16a(22) =17a(23) =33a(24) =18a(25) =34a(26) =35a(27) =19a(28) =39a(29) =40