The nonnegative integers.

Terms

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