A3. If you write the numbers $1 \mathrm{t} / \mathrm{m} 12$ in sequence, you get the number 123456789101112, which consists of 15 digits. If you write the numbers $1 \mathrm{t} / \mathrm{m} n$ in sequence, then you get a number that consists of 1788 digits.

What is the value of $n$?
(A) 533
(B) 632
(C) 645
(D) 1599
(E) 1689
A3. The numbers $1 \mathrm{t} / \mathrm{m} 9$ written consecutively are nine digits. The numbers $10 \mathrm{t} / \mathrm{m} 99$ written consecutively are 90 numbers of two digits, thus a total of 180 digits. Together, that makes 189 digits. $1788-189=1599$. Therefore, there are 1599:3=533 numbers of three digits written, starting with 100. So $n=99+533=632$.