IEEEXtreme 18.0 was held yesterday, and there are problems to upsolve, so let's discuss them here.

If there's a problem you couldn't solve mention it in a comment and someone might help you.

I'll start, in the problem Power of three I couldn't get past 60%, I tried looking for any special properties of powers of 3 that I can use to solve for large numbers but I couldn't find anything that is unique to powers of 3 other than the 2nd to last digit being even and the last digit being either 1, 3, 9 or 7. That still doesn't reach the answer though, if anyone solved it could you share the idea?.