 Perfection quotient

The ratio of the sum of the positive divisors of a positive integer to that integer. For coprime $a,b$, the ratio is multiplicative because the divisor function $\sigma$ is multiplicative. The contribution of a prime power $p^e$ is $(1+p+\cdots +p^e)/p^e$, so a prescribed quotient can be searched through its remaining numerator and denominator.