Problem Archive

Let $f(n)$ be the number of $6$-tuples $(x_1,x_2,x_3,x_4,x_5,x_6)$ such that:

• All $x_i$ are integers with $0 \leq x_i < n$
• $\gcd(x_1^2+x_2^2+x_3^2+x_4^2+x_5^2+x_6^2,\ n^2)=1$

Let $\displaystyle G(n)=\displaystyle\sum_{k=1}^n \frac{f(k)}{k^2\varphi(k)}$
where $\varphi(n)$ is Euler's totient function.

For example, $G(10)=3053$ and $G(10^5) \equiv 157612967 \pmod{1\,000\,000\,007}$.

Find $G(10^{12})\bmod 1\,000\,000\,007$.