Search ProblemsRSS Feed

Subset sums

Problem 635 Published on Saturday, 25th August 2018, 07:00 pm; Solved by 184

Let $A_q(n)$ be the number of subsets, $B$, of the set $\{1, 2, ..., q \cdot n\}$ that satisfy two conditions:
1) $B$ has exactly $n$ elements;
2) the sum of the elements of $B$ is divisible by $n$.

E.g. $A_2(5)=52$ and $A_3(5)=603$.

Let $S_q(L)$ be $\sum A_q(p)$ where the sum is taken over all primes $p \le L$.
E.g. $S_2(10)=554$, $S_2(100)$ mod $1\,000\,000\,009=100433628$ and
$S_3(100)$ mod $1\,000\,000\,009=855618282$.

Find $S_2(10^8)+S_3(10^8)$. Give your answer modulo $1\,000\,000\,009$.