高中数学题，请聪明的高手帮忙解答，（有点难）我穷没分的哦

(1)一位数1个：6，两位数6个：15.24.33.42.51.60，三位数21个：105.114.123.132.141.150.204.213.222.231.240.303.312.321.330.402.411.420.501.510.600，四位数前23个：1005.1014.1023.1032.1041.1050.1104.1113.1122.1131.1140.1203.1212.1221.1230.1302.1311.1320.1401.1410.1500.2004.2013，共51个数，