\(\dfrac{18}4=4+\dfrac24\)
which means 18 can be divided by a higher power of 4 to get a quotient smaller than 4. Indeed,
\(\dfrac{18}{4^2}=\dfrac{18}{16}=1+\dfrac24\)
Now divide the remainder by 4 gives
\(\dfrac24=0+\dfrac24\)
and so
\(18_{10}=102_4\)
Now the next four numbers are easy to find.
\(19_{10}=103_4\)
\(20_{10}=110_4\)
\(21_{10}=111_4\)
\(22_{10}=112_4\)
\(23_{10}=113_4\)
