2787. Ways to Express an Integer as Sum of Powers

Given two positive integers n and x. Return the number of ways n can be expressed as the sum of the xth power of unique positive integers, in other words, the number of sets of unique integers [n1, n2, ..., nk] where n = n1x + n2x + ... + nkx. Since the result can be very large, return it modulo 109 + 7. For example, if n = 160 and x = 3, one way to express n is n = 23 + 33 + 53. Example 1: