Squarefree part ($\mathrm{sf}(n)={\prod }_{v_p(n)\text{ odd}}p$)

The squarefree part of a positive integer $n$ is the unique squarefree integer $s$ such that $n=s{t}^2$ for a positive integer $t$. For example, the squarefree part of $72=2^3{3}^2$ is $2$. It retains precisely the primes with odd prime exponents; the radical of an integer instead retains every distinct prime factor.