Maybe because you put small numbers on your laptop while Codewars gives you huge numbers.
if you want to test something, make sure they're equal.

In this kata, there are 100 random tests. Each n and m consists of 8 digits numbers.

You'll need to get a little clever with performance, since n can be a very large number

Any idea why my solution keeps timing out? I timed it on my laptop and it took no time at all to complete while codewars keeps giving me an over 7000ms time out.