a(n) is the concatenation of 3n-2, 3n and 3n-1.

Terms

a(0) =132a(1) =465a(2) =798a(3) =101211a(4) =131514a(5) =161817a(6) =192120a(7) =222423a(8) =252726a(9) =283029a(10) =313332a(11) =343635a(12) =373938a(13) =404241a(14) =434544a(15) =464847a(16) =495150a(17) =525453a(18) =555756a(19) =586059a(20) =616362a(21) =646665a(22) =676968a(23) =707271a(24) =737574a(25) =767877a(26) =798180a(27) =828483a(28) =858786a(29) =889089