# negative base

The use of a negative base to represent
numbers gives rise to some intriguing possibilities. Consider "negadecimal,"
for example, in which the base is *minus* 10 instead of the familiar
positive 10. In this system, the number 365 is equivalent to the decimal
number 5 + (6 × -10) + (3 × -10 × -10), = 245, while 35 in
negadecimal is equivalent to 5 + (3 × -10), = -25, in ordinary decimal.
This points to an interesting fact: the negadecimal equivalent of any positive
or negative decimal number is always positive and therefore doesn't need
to be accompanied by a sign. The Polish UMC-1, of which a few dozen were
built in the late 1950s and earlier 1960s, is the only computer ever to
use "negabinary" (base 2 arithmetic).