由题意,一位数:6;二位数:15,24,33,42,51,60;三位数:105,114,123,132,141,150,204,213,222,231,240,303,312,321,330,402,411,420,501,510,600;四位数:1005,1014,1023,1032,1041,1050,1104,1113,1122,1131,1140,1203,1212,1221,1230,1302,1311,1320,1401,1410,1500,2004,2013
2013为第52个数,所以n=52
故选C.