Does Sage have an integer_root(x, n) function which reliable (!) returns floor(root(x,n)) for n-th roots? I think that it should be offered as a Sage function if not.
This seems to work:
def integer_root(x, n): return gp('sqrtnint(%d,%d)' %(x,n))
Integer n-th root of x, where x is non-negative integer.
// Related: question 10730.