I want to find any (nontrivial) necessary (and also sufficient, if possible) condition to determine whether $(p,q,r)$-pretzel link is equivalent to the trivial knot, where $p$, $q$, $r$ are integers.
I tried to find necessary conditions using knot polynomials, but for me, the calculations were so complicated.
Are there any already-known sources/references about solutions to it?