Find the missing term The sequence $10000, 121, 100, 31, 24, n, 20$ represents a number $x$ with respect to different bases. What is the missing number, $n$?
This is from my elementary computer aptitude paper. Is there any way to solve this quickly?

If the base in the last term is $b$, the number is $2b$.  The missing term is then in base $b-1$.  Expressed in base $b-1$ the integer is $2(b-1)+2=22$  The third to last term shows that $b-2 \ge 5$ so we are safe from a carry.
