Number of integer solutions to $a_1\ge a_2\ge\ldots\ge a_i\gt 0$ such that $a_1+a_2+\ldots+a_i=n$
Number of solutions to $a_1 + a_2 + \dots + a_k = n$ where $n \gt 0$ and $0 \lt a_1 \leq a_2 \leq \dots \leq a_k$ are integers.