(1/2)*(s(n) + 1), where s(n) is the n-th odd number in A026262.

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =6a(5) =7a(6) =5a(7) =8a(8) =9a(9) =15a(10) =10a(11) =16a(12) =11a(13) =17a(14) =18a(15) =12a(16) =13a(17) =14a(18) =25a(19) =26a(20) =27a(21) =28a(22) =19a(23) =20a(24) =21a(25) =22a(26) =34a(27) =23a(28) =35a(29) =36