Well-order the rational numbers; take numerators.

Terms

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