999...999 × 888...888
= 888...888 ×(1000...000 - 1)
= 888...888 000...000 - 888...888
= 888...887 000...000 + 1000...000 - 888...888
= 888...887 000...000 + 111...112
= 888...887 111...112
即1999个8、1个7、1999个1、1个2
各位数字和 = 2000*8 - 1 + 2000*1 + 1 = 2000* 9 = 18000