Question 1010135
Three-digit number, so factorization should be an easy chore.  Look to find that  7+2+9=18, a multiple of 3, so try to completely factorize...


{{{729=3*243=3*3*81=3*3*9*9=3*3*3*3*3*3}}}

You should see what the exponent is on the base of 3.


If it is the calculator skill you want, then that's a little different.  No key on a calculator (scientific nor graphical) for this.


Something else you might try is start with 3, the base, and find successive powers of 3.  You "might" get 729 or something near to it.  If not, then you may want to learn about logarithms (but that is not needed for the example you asked).