That's what happened when the
<input, output> pairs of any problem can be exhausted. In other words, as long as the mapping behavior of a function is fixed, one cannot distinguish how the function is actually implemented.
def checkPerfectNumber(self, num): return num in [6, 28, 496, 8128, 33550336]
For example, given integer
n > 0, write a function to return
x^n + y^n = z^n has positive integer solution
(x, y, z).