Natural numbers, pairs reversed: a(n) = n + (-1)^n; also Nimsum n + 1.

Terms

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