Take the list 1,2,3,4,... and replace each n with all d > 1 that divide n.

Terms

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