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$5$-smooth Totients

 Published on Sunday, 17th May 2015, 10:00 am and solved by 2031
Difficulty: Level 8 [22%]

Problem 516

$5$-smooth numbers are numbers whose largest prime factor doesn't exceed $5$.
$5$-smooth numbers are also called Hamming numbers.
Let $S(L)$ be the sum of the numbers $n$ not exceeding $L$ such that Euler's totient function $\phi(n)$ is a Hamming number.
$S(100)=3728$.

Find $S(10^{12})$. Give your answer modulo $2^{32}$.



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