Concatenate (3n-2,3n-1,3n).

Terms

a(0) =123a(1) =456a(2) =789a(3) =101112a(4) =131415a(5) =161718a(6) =192021a(7) =222324a(8) =252627a(9) =282930a(10) =313233a(11) =343536a(12) =373839a(13) =404142a(14) =434445a(15) =464748a(16) =495051a(17) =525354a(18) =555657a(19) =585960a(20) =616263a(21) =646566a(22) =676869a(23) =707172a(24) =737475a(25) =767778a(26) =798081a(27) =828384a(28) =858687a(29) =888990