Xavier, a 9-year-old student, loves playing many kinds of puzzles. One of his favourites is the following:
Xerier, his classmate, has made many cards. She writes down a single positive number on each of them. No numbers written on different cards are the same. After that she writes down an equation, whose right side is a single positive number chosen by her, and the left side is the sum of p integers:
Then she asks Xavier put p cards on the corresponding Xi’s position to make this equation correct, with an additional condition that Xi should be ordered from smaller to bigger, i.e.
Every time Xavier immediately comes up with many solutions. Now he wants to know how many solutions in total are there for any n given by Xerier.