
Counting Tuples
Let $\pi(x)$ be the prime counting function, i.e. the number of prime numbers less than or equal to $x$.
For example,$\pi(1)=0$, $\pi(2)=1$, $\pi(100)=25$.
Let $T(n, k)$ be the number of $k$-tuples $(x_1, \dots, x_k)$ which satisfy:
1. every $x_i$ is a positive integer;
2. $\displaystyle \sum_{i=1}^k \pi(x_i)=n$
For example $T(3,3)=19$.
The $19$ tuples are $(1,1,5)$, $(1,5,1)$, $(5,1,1)$, $(1,1,6)$, $(1,6,1)$, $(6,1,1)$, $(1,2,3)$, $(1,3,2)$, $(2,1,3)$, $(2,3,1)$, $(3,1,2)$, $(3,2,1)$, $(1,2,4)$, $(1,4,2)$, $(2,1,4)$, $(2,4,1)$, $(4,1,2)$, $(4,2,1)$, $(2,2,2)$.
You are given $T(10, 10) = 869\,985$ and $T(10^3,10^3) \equiv 578\,270\,566 \pmod{1\,004\,535\,809}$.
Find $T(20\,000, 20\,000) \pmod{1\,004\,535\,809}$.