Perfect power
A positive integer is a perfect power if there exist integers such that and . In particular, is said to be a perfect th power. For example, , so 64 is a perfect 2nd, 3rd and 6th power.
We restrict only because "being a perfect st power" is a meaningless property: every integer is a st power of itself.
Perfect second powers are usually known as perfect squares and perfect third powers are usually known as perfect cubes. This is because the area of a square (volume of a cube) with integer edge is equal to the second (respectively third) power of that edge, and so is a perfect second (respectively third) power.