次方数（英语：square）也称为幂次数，是指一正整数n可以表示为另一正整数的平方、立方或更高次方。n为次方数的条件是存在正整数m > 1及k > 1使得m = n，此时n可以称为完全k次方数，若k = 2或k = 3，n可以称为平方数或立方数。由于针对任意正整数k，1 = 1均成立，因此有时也将1视为次方数。

In mathematics, a perfect power is a positive integer that can be expressed as an integer power of another positive integer. More formally, n is a perfect power if there exist natural numbers m > 1, and k > 1 such that m = n. In this case, n may be called a perfect kth power. If k = 2 or k = 3, then n is called a perfect square or perfect cube, respectively. Sometimes 1 is also considered a perfect power (1 = 1 for any k).