Negative bases

Given a suitable list of digits from 0 to k-1 one can obtain any positive or negative number using FromDigits[list, -k]. The picture below shows the digit sequences of successive numbers in base -2; the row j from the bottom turns out to consist of alternating black and white blocks of length 2^{j}. (In ordinary base 2 a number -n can be represented as on a typical electronic computer by complementing each digit, including leading 0's.) (See also page 1093.)