Concatenation of n and n + 8 or {n,n+8}.

Terms

a(0) =19a(1) =210a(2) =311a(3) =412a(4) =513a(5) =614a(6) =715a(7) =816a(8) =917a(9) =1018a(10) =1119a(11) =1220a(12) =1321a(13) =1422a(14) =1523a(15) =1624a(16) =1725a(17) =1826a(18) =1927a(19) =2028a(20) =2129a(21) =2230a(22) =2331a(23) =2432a(24) =2533a(25) =2634a(26) =2735a(27) =2836a(28) =2937a(29) =3038