Review question

# What's the smallest number with four different prime factors? Add to your resource collection Remove from your resource collection Add notes to this resource View your notes for this resource

Ref: R7162

## Question

$f(x)$ denotes the number of different prime factors of the integer $x$, excluding $1$ and $x$ itself. For example, since $12=2\times2\times3$, then $f(12)=2$.

1. Calculate $f(121)$.
2. Calculate $f(17)$.
3. Write down the smallest $x$ for which $f(x)=4$.