to denote the number
whose (base 10) digits are ak, ak−1, . . . , a1, a0 from left to right. In other
words, the sum in equation (1). Thus, if a = 2718 = [a3a2a1a0], then [a3a2] =
27. We will often use the fact that [akak−1 . . . a1a0] = 10n
[akak−1 . . . an] +
[an−1 . . . a0].