Count ways to express a number as sum of powers

Given two integers x and n, we need to find number of ways to express x as sum of n-th powers of unique natural numbers. It is given that 1 <= n <= 20.
Examples: 

Input : x = 100
 n = 2
Output : 3
Explanation: There are three ways to 
express 100 as sum of natural numbers
raised to power 2.
100 = 10^2 = 8^2+6^2 = 1^2+3^2+4^2+5^2+7^2

Input : x = 100
 n = 3
Output : 1
Explanation : The only combination is,
1^3 + 2^3 + 3^3 + 4^3

We use recursion to solve the problem. We first check one by one that the number is included in summation or not. 

Output: 

3

Time Complexity: O(2 ^ pow(x^(1/n))) 
Auxiliary Space: O(pow(x^(1/n))