Let $S_k$ be the set containing $2$ and $5$ and the first $k$ primes that end in $7$. For example, $S_3 = \{2,5,7,17,37\}$.
Define a $k$-Ruff number to be one that is not divisible by any element in $S_k$.
If $N_k$ is the product of the numbers in $S_k$ then define $F(k)$ to be the sum of all $k$-Ruff numbers less than $N_k$ that have last digit $7$. You are given $F(3) = 76101452$.
Find $F(97)$, give your answer modulo $1\,000\,000\,007$.
Solution
No solution yet. Write yours at
solutions/s773.md.