Fix 0; exchange even and odd numbers.

Terms

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