text: Exponentiation with base  is used in scientific notation to denote large or small numbers. For instance,  (the speed of light in vacuum, in metres per second) can be written as  and then approximated as .
  SI prefixes based on powers of  are also used to describe small or large quantities. For example, the prefix kilo means , so a kilometre is .
  Powers of two
  The first negative powers of  are commonly used, and have special names, e.g.: half and quarter.
  Powers of  appear in set theory, since a set with  members has a power set, the set of all of its subsets, which has  members.
  Integer powers of  are important in computer science. The positive integer powers  give the number of possible values for an -bit integer binary number; for example, a byte may take  different values. The binary number system expresses any number as a sum of powers of , and denotes it as a sequence of  and , separated by a binary point, where  indicates a power of  that appears in the sum; the exponent is determined by the place of this : the nonnegative exponents are the rank of the  on the left of the point (starting from ), and the negative exponents are determined by the rank on the right of the point.