(PHP 5 >= 5.6.0, PHP 7)
gmp_root — Take the integer part of nth root
$a
$nth
Takes the nth root of a and returns the integer component of the result.
nth
a
PHP 5.5 之前为 GMP 数值资源，PHP 5.6 之后为 GMP 对象或数字，或可以转为数字的字符串。
The positive root to take of a.
The integer component of the resultant root, as a GMP number.